Authorities. In the Acta Sanctorum Martii (Vol. I,
pp. 653-746) are to be found the sources from which the biographers of
St. Thomas draw the materials for the study of his life: the
Acts of the process of canonization, the Life by Tocco,
accounts of the translations of his remains, etc. Potthast
(Wegweiser durch die Geschichtswerke des Europäischen
Mittelalters, p. 1601) gives a complete list of sources. cf.
Vaughan, Life and Labors of S. Thomas of Aquin (2 vols., London,
Life. St. Thomas, surnamed the Angelic Doctor, belonged to the
noble family of Aquino, which was related to the imperial family and to
the royal houses of Aragon, Sicily, and France. His father was count of
Aquino, Belcastro, and Roccasecca. In the fortress at Roccasecca our
saint was born in the year 1224 or 1225.  When five years old he was
sent to the monastery of Monte Cassino, where his uncle Sinnebald ruled
as abbot. There, in the midst of the struggles between the papacy and
the empire, -- struggles in which the abbot, as feudal lord of a large
province, was obliged to take sides, -- the monks continued to teach
and to cultivate learning, and there, according to tradition, the young
Thomas began to occupy his mind with the question, Quid est
Deus? He studied grammar, poetry, rhetoric, logic, and, perhaps,
the elements of philosophy. In 1236 Sinnebald died, and shortly after
that event the community of Monte Cassino was broken up for a time, and
St. Thomas returned to his father's castle. After a brief sojourn at
home St. Thomas was sent to the University of Naples. The change from
Monte Cassino to the university was an important crisis in the life of
our saint. The university was at that time dominated by the influence
of Frederick II, an influence which was hostile to religion, or at
least to the papacy and to the mendicant orders. The city, if we are to
believe contemporary chroniclers, was a veritable hotbed of irreligion
and licentiousness. St. Thomas, uninfluenced by these surroundings,
continued to devote himself to his studies, having for masters Martinus
in grammar and Petrus Hibernus in natural science: "In quorum scholis,"
says Tocco, "tam luculenti coepit esse ingenii et perspicacis
intelligentiae ut altius et profundius et darius aliis audita repeteret
quam a suis doctoribus audivisset."
 The latter is, everything considered, the most probable date.
cf. Acta Sanctorum Martii, Vol. I, p. 656.
In 1243 Thomas entered the order of St. Dominic. His mother, Theadora,
having looked forward to another career for her son, threw every
obstacle in the way of his entering the Order of Preachers. She carried
her opposition so far as to imprison him in the fortress of San
Giovanni. Toward the end of the second year of his imprisonment Thomas
made his escape, and, the opposition on the part of his relatives
having ceased, he was allowed to proceed to Paris in the company of
John of Germany. He does not seem to have tarried at Paris for any
length of time, but to have gone at once to Cologne, where Albert was
teaching. This was in 1244 or 1245. Albert perceived at once the
extraordinary talents of his pupil, and when Thomas' fellow-students,
failing to detect the intellectual greatness hidden under an extreme
modesty of manner, surnamed him the "Dumb Ox," Albert foretold the
future renown of his pupil: "Nos vocamus istum bovem mutum, sed ipse
adhuc talem dabit in doctrina mugitum quod in toto mundo sonabit." 
Tocco  describes the student Thomas as
follows: "Coepit miro modo taciturnus esse in silentio, in studio
assiduus, in oratione devotus, interius colligens in memoria quad
postmodum effunderet in doctrina."
 Tocco, Vita, Cap. 3.
Soon after his arrival at Cologne, Thomas was sent to Paris in company
with Albert. There they remained until 1248. When, in 1248, Albert was
recalled to Cologne, it was decided that his illustrious pupil should
once more accompany him, and continue to study under his direction. In
1251 or 1252, by order of the General of the Dominicans, Thomas
repaired to Paris, where he undertook the task of expounding the
Books of Sentences. In 1256 (this is the most probable date) 
St. Thomas received the degree of master, and was placed at the head of
the school at St. James as regens primarius. It is probable,
however, that, on account of the conflict between the mendicants and
the seculars, the solemn inceptio did not take place until 1257.
Mention has already been made of the part which St. Bonaventure and St.
Thomas took in the controversy arising out of this dispute and in the
efforts of the mendicants to secure a favorable decision from Rome.
 1253 is the date given by the Bollandists, op. cit., p. 656.
Denifle (Chartul., I, 307, n.) gives the following dates: 1248,
St. Thomas was sent to Cologne; 1251-1252, he explained the Books of
Sentences at Paris; 1256, he was made master in theology.
While fulfilling his task as bachelor, or assistant professor, St.
Thomas composed his Commentaries on the Books of Sentences.
After his promotion to the duties of master of sacred science he
continued to teach and write, taking up special points treated in
elementary fashion by the bachelor who taught under his direction, and
devoting himself to the thorough discussion of each doctrine in all its
bearings. His fame as a teacher rapidly spread throughout Europe and,
in obedience to the commands of his superiors, he taught successively
at Rome, Bologna, Viterbo, Perugia, and Naples. In his lectures as well
as in his writings, St. Thomas was actuated by a twofold purpose: he
strove, first, to defend the truth against the attacks of its enemies,
and, secondly, to build up a system of theology and philosophy. The
Summa contra Gentiles and the Summa Theologica are proof
of his ability both as an apologist and as a constructive thinker. The
former work, begun at Paris about the year 1257 and completed sometime
between the years 1261 and 1264, was undertaken at the request of St.
Raymund of Pennafort for the purpose of defending Catholic truth
against the Arabian pantheists and their followers. The latter work was
begun at Bologna about the year 1271. It is St. Thomas' greatest work,
his last and most important contribution to Christian theology and
philosophy. For, though the work is entitled Summa Theologica,
and is, in fact, a summary of Catholic theology, it is also a summary
of philosophy. It begins with the question of the existence of God,
treats of the attributes of God, traces the process of things from God,
and the return of man to God through Christ by means of the sacraments
which Christ instituted. It treats, therefore, of the creation and
government of the universe, of the origin and nature of man, of human
destiny, of virtues, vices, and laws -- of all the great problems of
speculative and practical philosophy. It is the key to the thought of
St. Thomas: it contains the views of his more mature years, and
whenever discrepancies occur between the doctrines of the Summa
and the views expressed in his earlier works, the Summa is
always to be taken as the embodiment of the "mind" of St. Thomas.
During his career as professor, St. Thomas composed also the
Quaestiones Disputatae and the Quodlibeta. When a
problem, arising out of the interpretation of Aristotle or of the
Lombard, was so complicated that its discussion would occupy too much
space in the Scholastic commentary, or was so difficult as to puzzle
the bachelor, whose duty it was to expound the text of Aristotle or of
the Lombard, it was made the subject of a special treatise by the
master, and such treatises were called Quaestiones Disputatae.
The Quodlibeta were answers to questions put to the master by
pupils or by outsiders. When, therefore, we find the following among
the questions answered by St. Thomas: Did St. Peter sin mortally when
he denied Christ? Does a crusader who is returning from the Holy Land
die a better death than one who is going thither? Do the damned rejoice
at the sufferings of their enemies?  we should admire the gentle
forbearance with which he strove to remove the difficulties that lay in
the way of minds less gifted than his.
 Cf. Quodlibeta, IX, 5 VIII, 16; III, 24.
After the completion of the first and second parts of the Summa
Theologica, St. Thomas took up his abode at the convent of his
order in Naples and there devoted himself to the completion of the
third part. At the end of a year and a half, having reached the
ninetieth question, he felt that he could proceed no farther with the
work, and when his faithful friend Reginald urged him to continue, he
answered in all simplicity, "Non possum." In obedience, however, to the
command of Gregory X, he set out for Lyons at the beginning of the year
1274 in order to attend the council that was being held in that city.
He fell sick on the way, and when the Cistercian monks of Fossa Nuova,
near Maienza, invited him to their cloister, he accepted their
invitation. There he spent the last days of his life among the sons of
St. Benedict, whose brethren at Monte Cassino had watched
over his early education, and there, on March 7, he died while
expounding the Canticle of Canticles.
Character. Contemporary biographers and the witnesses whose
depositions are to be found in the Acts of canonization bear
testimony to the exalted sanctity of the Angelic Doctor; the Pange
lingua, the Lauda Sion, and the prayers which he composed
for the office of the Blessed Sacrament testify to his great piety.
Every page of his philosophical and theological works reveals the
author's single-minded devotion to truth, his courtesy towards his
opponents, and his extraordinary grasp of the great principles of
Scholastic philosophy and theology. Tocco describes him as "magnus in
corpore et rectae staturae quae rectitudini animae respondet . . . animum
nulla sensualis passio perturbabat, nullius rei premebat affectio
temporalis, nec ullius honoris inflabat ambitio . . . intro modo
contemplativus et coelestibus deditus." 
 Vita, Cap. 7. cf. Muratori, Rerum Italicarum
Scriptores, XI, 1153.
Sources. The principal editions of the works of St. Thomas are
the following: the Roman edition of 1570 (known as the edition of Pius
V), the Venetian edition of 1592, the Paris edition of 1660, the Parma
edition of 1852, and the Leonine edition begun by the Dominicans at
Rome in 1882 by order of Leo XIII. The works of St. Thomas may be
grouped as follows: (1) commentaries on the works of Aristotle; (2)
commentaries on the Books of Sentences; (3) exegetical works, i.e.,
commentaries on the Scriptures, and collections of the opinions of
Patristic exponents of the text (Catena Aurea); (4) commentaries
on the Pseudo-Dionysian treatise De Divinis Nominibus, and on
the Boethian treatises De Hebdomadibus and De Trinitate;
(5) Summa contra Gentiles, Summa Theologica, Quaestiones Disputatae
Opuscula, and Quodlibeta.
On the question of the genuineness of the works ascribed to St. Thomas,
cf. the Dissertatio Critica by De Rubeis, which is prefixed to the
Leonine and other editions.
PHILOSOPHY OF ST. THOMAS
In treating of the philosophical system of St. Thomas it will be found
convenient to consider: (1) St. Thomas' notion of science, doctrine of
the interrelation of sciences, doctrine of universals, theory of
knowledge; (2) logic; (3) anthropology; (4) cosmology; (5) metaphysics,
including natural theology; and (6) moral and political doctrines.
1. Notion of Science, etc. (a) Science is the knowledge
of things through their causes. Scientific knowledge differs from
knowledge in general in this, that it gives the cause, or wherefore, of
a phenomenon or event. It is, therefore, defined as a knowledge of
principles;  for, when we define science as a knowledge through
causes, we mean primarily those intrinsic causes, or principles, which
constitute the unalterable natures of things and underlie their
external, shifting, sense-perceived qualities. And, since it is on the
unalterable natures of things that laws are based, science may be
defined as the knowledge of laws: it is concerned with what is
changeable and contingent in so far as the changeable and contingent
contains the necessary and universal, which is the true object of
scientific knowledge. 
 Sum. Theol., Ia IIae, I, 5, c.
(b) Faith and Reason. Intimately associated with the notion of
science is the notion of truth. Truth is defined as "adaequatio rei et
intellectus."  Now God is the source of all truth. He communicates it
to us directly by revelation and indirectly by giving us the power by
which we acquire it. Science acquired in the former manner would be
divine, while the science which we ourselves derive from experience and
reason is human. Theology is partly divine and partly human. It is
divine in its origin, for it starts with revealed truths as principles;
and it is human in the course of its development, for it proceeds from
premise to conclusion by the aid of reason. The distinction between
divine science and human science is not a distinction of material
objects, that is, of the truths with which each is concerned, but
rather a distinction of formal objects, that is, of the point of view
from which the same truths are studied in each science. The difference
between theology and philosophy does not consist in the fact that
theology treats of God, for philosophy also treats of God and divine
truths; the distinction consists rather in this, that theology views
truth in the light of divine
revelation, while philosophy views truth in the light of human reason.
This is the first and broadest distinction between theology and
 Op. cit., Ia, LXXXIV, 1, c.
 Op. cit., Ia, XXI, 2, c.
There are truths which belong exclusively to theology, there are truths
which belong properly to philosophy, and there are truths which are
common to both sciences. The truths which belong exclusively to
theology are the mysteries of faith, such as the Incarnation and the
Trinity, which the human mind can neither demonstrate nor comprehend.
These we know on the authority of God, Who revealed them. The truths
which belong exclusively to philosophy are natural truths of the lower
order; that is, truths which have no bearing on man's destiny or on his
relations with God. The truths which belong to both sciences are
natural truths of the higher order, such as the existence of God.
These, on account of the important relation which they bear to
supernatural truth, are called the praeambula fidei. They come
within the scope and power of natural reason, and are, therefore,
natural; nevertheless, they are proposed for our belief, for, though a
knowledge of them is possible to all men, it is in point of fact
attained only by a few (a paucis, et per longum tempus et cum
admixtione multorum errorum). Considering, on the one hand, the
vital importance of these truths, and, on the other hand, the
difficulty of attaining a knowledge of them, it seems natural and
fitting that God in His goodness should propose them for our
belief.  Now, whether we consider the truths which belong
exclusively to theology, or those which are common to theology and
philosophy, we realize that the science which studies both classes of
truths in the light of revelation, and the science which studies the
latter class of truths in the light of reason, are distinct
 Op. cit., Ia, I, i, ad 2um.
 C. G., I, 3, 4; cf. Gonzalez, op. cit., II, 228.
But while it is certain that theology and philosophy are distinct, it
is no less certain that they are in complete harmony one with the
other. "Ea quae ex revelatione divina per fidem
tenentur non possunt naturali cognitioni esse contraria."  This
principle, which may be said to be implied in every system of Christian
speculation, is explicitly proved  by the following consideration: God
is the author of all knowledge, natural as well as revealed. It is,
therefore, He who teaches us, not only when, by means of the revelation
which He has vouchsafed to grant us, we attain the knowledge of truth
in the supernatural order, but also when, by the natural powers, which
also are His gift, we discover truth in the natural order. Now it is
impossible that God should contradict Himself; it is, therefore,
impossible that there should exist a contradiction between natural
truth and truth of the supernatural order.
 C. G., I, 7.
But this is not all. Not only does faith not contradict reason; it
strengthens and supplements reason. Faith introduces us into a new
world of truth, into a world where everything is novel and strange, but
where, nevertheless, an Intelligent Ruler reigns; where, consequently,
we find that everything obeys the inexorable laws of thought which rule
the natural world; for a mystery is not a contradiction. Thus is the
horizon of knowable truth enlarged by revelation, and faith becomes the
complement of reason. St. Thomas was fully convinced of the limitations
of human thought. He did not, it is true, draw the limits of thought so
closely as Mansel and Spencer have done. He possessed more confidence
than they in the power of the human mind to attain truth. Still, he
recognized the principle that the human mind, however high it may soar,
must sometime or other reach a level beyond which it cannot rise, and
at which all natural knowledge ends. He differed, however, from the
agnostic (and the difference is radical) in this, -- that while beyond
the region of knowledge the modern philosopher places the region of
nescience, St. Thomas taught that where science ends faith begins, and
that faith is a kind of knowledge. Faith is the assent to truth on
account of the authority of God:
 Loc. cit.
Assentit autem intellectus alicui dupliciter, uno modo quia ad hoc
movetur ab ipso objecto quod est per seipsum cognitum, sicut patet in
primis principiis, quorum est intellectus, vel per aliud
cognitum, sicut patet in conclusionibus, quarum est scientia.
Alio modo intellectus assentit alicui, non quia sufficienter movetur ab
objecto proprio sed per quamdam electionem voluntarie declinans in unam
partem . . . et si quidem hoc sit cum dubitatione et formidine alterius
partis, erit opinio, si autem sit cum certitudine, absque tali
formidine, erit fides.
 Sum. Theol., IIa IIae, I, 4, c; cf. Quaestio
Disputata De Veritate, XIV, 1, c.
Faith, therefore, in so far as it depends on the will is meritorious,
while in so far as it is a firm assent and excludes doubt it adds to
our knowledge. Knowledge, coextensive with reality, is divided into the
realm of science and the realm of faith, and these realms are
continuous. Moreover, all faith is radically reasonable; for belief
rests on the authority of God, and reason tells us that God can neither
deceive nor be deceived:
Dicendum quod ea quae subsunt fidei dupliciter considerari possunt: uno
modo, in speciali, et sic non possunt esse simul visa et credita
alio modo in generali, scilicet sub communi ratione credibilis,
et sic sunt visa ab eo qui credit. Non enim crederet nisi videret ea
esse credenda. 
 Sum. Theol., IIa IIae, I, 4, ad 2um.
From the foregoing principles it follows that science can aid faith (1)
by furnishing the motives of credibility and by establishing the
preambles of faith; (2) by supplying analogies which enable us to
represent to ourselves truths of the supernatural order; (3) by solving
the objections which the opponents of faith urge against supernatural
truth. St. Thomas subscribed to the twofold principle of Scholasticism:
Credo ut intelligam; intelligo ut credam.
St. Thomas' doctrine concerning the relations between revelation and
reason may be summed up in the propositions: (1) the domain of faith is
distinct from the domain of reason; (2) the former is a continuation
of the latter. Here we find expressed the thought which agitated the
minds of the schoolmen during the first two periods of Scholasticism --
the thought, namely, that revelation is reasonable and that reason is divine. This thought,
which was held in solution in every system of Scholasticism from the
extreme mysticism of Erigena to the extreme rationalism of Abelard
(both of whom, though for different reasons, identified theology with
philosophy), is now at last crystallized, and the Protestant as well as
the Catholic apologist of Christianity will to-day acknowledge that
nowhere can there be found a better statement of the relation between
revelation and reason than in the principles formulated by St. Thomas.
The doctrine of St. Thomas on this point is of interest not merely to
the apologist, but also to the philosopher; for every effort at
philosophical construction is an effort at establishing continuity. The
Greeks, while they distinguished mind and matter, taught that there
exists no antagonism between them, and it was in a similar spirit of
constructive synthesis that St. Thomas, while clearly distinguishing
the province of theology from that of philosophy, established once for
all the continuity of the supernatural with the natural, of revelation
with reason. It is this aspect of the question that gives it its
importance in the history of philosophy. 
 Cf. Cath. Univ. Bull. (July, 1896), Vol. II, pp. 188
(c) Division of sciences. St. Thomas divides the sciences, in
accordance with Aristotle's scheme of classification, into physical,
mathematical, and metaphysical.  All science is abstraction, that is,
separation, or analysis, of the complex totality of phenomena; the
physical, mathematical, and metaphysical sciences represent ascending
grades of abstraction. 
 In VIum Metaphyricorum, Text. 2,
(d) Doctrine of universals. All science is concerned with the
abstract and, therefore, with the universal: of singular things, in so
far as they are singular, there is no science. But the universal,
though abstract, is real. St. Thomas regards the nominalist denial of
the reality of universals as a denial of the reality
of all science. He does not, however, agree with the Platonic
realists, who teach that the universal exists outside the mind as a
universal, in the same way as it exists in the mind. The universal
existed ante rem in the mind of God, as exemplar cause; it
exists post rem in the human mind, as an idea or image extracted
from concrete things; and it exists in re, as the essence or
quiddity of things; but the universal in re is not formally
universal: the mind, reflecting that the universal quiddity is
predicable of many, invests this quiddity with the formal aspect of
 Cf. Opusc., XXXIV; in Roman edition, LXX, Q. V, Art.
Quod est commune multis non est aliquid praeter multa nisi sola
ratione.  Cum dicitur universale abstractum, duo intelliguntur,
scilicet ipsa natura rei et abstractio seu universalitas. Ipsa igitur
natura rei cui accidit vel intelligi vel abstrahi vel intentio
universalitatis, non est nisi in singularibus: sed hoc ipsum quod est
intelligi vel abstrahi vel intentio universalitatis, est in
Licet natura generis et speciei numquam sit nisi in his individuis,
intelligit tamen intellectus naturam speciei et generis non
intelligendo principia individuantia: et hoc est intelligere
Universalia, secundum quod sunt universalia, non sunt nisi in anima.
Ipsae autem naturae, quibus accidit intentio universalitatis, sunt in
 Cf. p. 266.
The sciences, therefore, are real because the universal is real. The
sciences, however, differ in many respects: the same method is not to
be employed in different sciences, neither is the same certitude to be
sought in each.
 C. G., I, 26.
 Sum. Theol., Ia, LXXXV, 2, ad 2um.
 C. G., II, 75.
 In IIum De An., Lect. 12.
Ad hominem bene disciplinatum, id est, bene instructum, pertinet ut
tantum certitudinis quaerat in unaquaque materia quantum natura rei
 In Ium Ethicorum, Lect. 3.
Theology rests on the authority of revelation; in the other sciences
the principal means of arriving at truth is the use of our own reason
and the employment of induction or deduction, according to the nature
of the science. Authority holds a very unimportant place:
"Studium sapientiae non est ad hoc quod
sciatur quid homines senserint, sed qualiter se habeat veritas
rerum."  St. Thomas maintains that in matters scientific the argument
from authority is the weakest of all arguments,  and thus condemns
those who would solve the problems of philosophy by an appeal to the
works of Aristotle or of some other master.
 De Coelo et Mundo, I, Lect. 22.
(e) Theory of knowledge. St. Thomas' theory of knowledge is
conditioned by his psychological doctrines. It is possible, however, to
describe his epistemological doctrines in general terms without
entering, for the present, into an account of his psychological system.
 "Locus ab auctoritate quae fundatur super ratione humana est
infirmissimus." Sum. Theol., Ia, I, 8, ad 2um
All knowledge begins with sense-knowledge.  The senses, the
intellectual faculties, and the authority of others are the sources of
our knowledge, and, in normal conditions, they are reliable sources.
With respect to the senses, St. Thomas, following Aristotle,
distinguishes four classes of objects, the sensibile per se, the
sensibile per accidens, the sensibile proprium, and the
sensibile commune.  The sensibilia propria are color,
taste, sound, etc., and the sensibilia communia are size,
motion, shape, etc. The former exist potentially in the object,
independently of the sense; actually, however, taste, for example, does
not exist except when it is perceived.  But, while St. Thomas makes
this concession to idealism, he maintains, in opposition to the
fundamental tenet of the idealists, that what we first perceive is not
the mental process, which takes place within us, but the physical
counterpart of that process, which exists in the world outside us. He
is an advocate of presentative, or immediate, as opposed
to representative, or mediate, perception: he teaches
that the senses are in immediate contact with the object, as far as
consciousness is concerned, although, as we shall see, he holds that between the senses and the object there are
certain media of communication (species sensibiles), which do
not appear in direct consciousness.
 Op. cit., Ia, LXXVIII, 4, ad 4um.
 Op. cit., Ia, XVII, 2, c.
 In IIum De An., Lect. 16.
Quidam posuerunt quod sensus non sentit nisi passionem sul organi sed
haec opinio manifeste apparet falsa. . . . Species secundario
est id quod intelligitur: id quod intelligitur primo est
 Sum. Theol., Ia, LXXXV, 2.
He explains the illusions of sense by referring them to one or
other of the following causes: (1) the sense-organ is not in its normal
condition; (2) it is a question of a sensibile per accidens, not
of a sensibile per se.  With regard to the sensibilia
communia, St. Thomas does not realize the important part played by
interpretation in processes which are apparently cases of intuitive
perception. He admits, however, the fact that interpretation plays a
part in these processes: "Naturas sensibilium qualitatum cognoscere non
est sensus sed intellectus." 
 Op cit., Ia, XVII, 2, c.
Intellectual knowledge is derived from sense-knowledge. The intellect,
by its immaterial energy, separates, or puts aside, all the material
conditions of the sense-image, leaving the immutable, universal element
which represents itself on the mind as an immaterial idea. The process
is one of abstraction or separation. If, then,
sense-knowledge is a source of truth, intellectual knowledge is also a
source of truth; for the mind adds nothing to the sense-image; it
merely brings to light the intellectual element therein contained. 
 Op. cit., Ia, LXXVIII, 3, c.
 Cf. op. cit., Ia, LXXVI, 2, ad
But, though it is customary to speak of the truth of the senses and of
the truth of the act by which the intellect abstracts universal ideas,
yet truth full-fledged, so to say, is not found except in judgment and
reasoning.  Now, we form a judgment by virtue of an innate power of the
mind, by what may be called a natural sensitiveness to the light of
evidence, -- and propositions, as they present themselves to us, are
evident either immediately or through the medium of other and more evident
propositions. In this way, by the power of judgment, we arrive at a
knowledge of first principles, and at a knowledge of conclusions
which, when organized, is properly called science.
 Q. Disp. De Ver., I, 3.
But what is knowledge? St. Thomas describes it as a vital process in
which the subject is rendered like the object by a process of
information: "Omnis cognitio fit per assimilationem cognoscentis
et cogniti."  He likens it to the process by which the seal impresses
its form on the wax. The object, whether it be composed of matter and
form or be pure form, is what it is by virtue of the form. Now, when
the object becomes known, it impresses its form on the mind, causing
the mind not to be the object, but to know the object. Moreover, in the
act of knowledge, subject and object become one in the ideal order, 
-- an expression which means merely that the object becomes known by
us and we become knowing the object. Beyond these somewhat general
expressions St. Thomas does not attempt to describe the nature of
knowledge, realizing perhaps the impossibility of describing knowledge
in terms more elementary than the term knowledge itself.
 C. G., I, 65.
2. Logic. In logic, St. Thomas did not make any notable addition
to the doctrine of Aristotle. The opusculum entitled Summa
Totius Logicae, which was ascribed to St. Thomas, is the work of
some disciple of the saint, perhaps of Hervé of Nedellec (died
1323). It is a compendium of the treatises which formed the body of
Aristotelian logical doctrine.
 Cf. Sum. Theol., Ia, LV, 1, ad 2um.
3. Anthropology. The central doctrine in St. Thomas' teaching
concerning man is that of the substantial union of soul and body. Body
and soul are co-principles of the substantial unit which is man: they
are united as matter and form. Complete substantial nature belongs
neither to the soul alone nor to the body alone, but to the compound of
both: it is the compound which is and acts. It is by virtue of the soul
that man is a rational being, a substance, a being: it is by virtue of the soul that
the body has whatever it possesses. But just as the body requires the
soul in order to be what it is and to move and live, the soul requires
the body for its natural being and operation. It is true that the
soul is superior to matter, that in the highest operations of the mind
it is intrinsically independent of the body, and that it is capable of
surviving the body; but it is none the less true that there is no
operation of the soul, however high, in which the body has not its
share, and that, after its separation from the body, the soul is, as it
were, in an unnatural state until it is reunited with the body after
the body's resurrection. 
 Cf. In IIum De An., Lect.
The soul is defined as primum principium vitae in his quae
apud nos vivunt,  and life is defined as self-originating
motion: "Illud enim proprie vivere dicimus quod in seipso habet
principium motus vel operationis cujuscumque."  Thus, although the
eye, the heart, etc., are principles of vital functions, they are not
the radical principles of those functions; for if these, as bodies,
were the first principles of life, all bodies would be endowed
with life.  The soul is therefore the radical principle of all vital
 Q. Disp. De Anima, Art. 1, ad
4um; De Potentia, V, 10; De
Spiritualibus Creaturis, Art. 2, ad
 Sum. Theol., Ia, LXXV, 1, c.
Since life is the power of self-motion, or, as we should say,
the power of adaptation, living beings are arranged in a scale of
ascending perfection according to the degree in which they possess the
power of self-motion. In this way St. Thomas is led to distinguish
plant life, animal life, and intellectual life, and to this distinction
corresponds the distinction of vegetative soul, sensitive soul, and
rational soul.  All life is a triumph of form over matter, of activity
over inertia, of initiative force over indeterminateness, and the
greater the triumph the higher the form of life.
 Q. Disp. De Ver., IV, 8.
 Sum. Theol., Ia, LXXV, I.
 Op. cit., Ia, XVII, 3.
The soul, then (and by soul is meant not merely mind, but the principle
of all vital activity), is united substantially with the body.
The union is no mere accidental union, as Plato taught; for
consciousness tells us that it is the same substance which thinks and
speaks and moves and eats.  Neither are there forms intermediate
between soul and body, as the Neo-Platonists taught;  for although
there is no quantitative contact between soul and body, there is the
contact of immediate action and reaction (contactus virtutis),
as the facts of consciousness prove. Thus does St. Thomas, taking his
stand on the empirical principles of consciousness, simplify the
problems of epistemology by regarding man as the blending of what in
modern epistemology would be called self and not-self, and by refusing
to look upon subject and object as separated by that chasm which every
epistemologist since the days of Descartes has striven in vain to
 C. G., II, 56; Sum. Theol., Ia, LXXVI, 1, c.
The soul is one, inextended, immaterial. Its immateriality is proved by
the fact that in its intellectual operations it rises above all
material conditions. It is present in every part of the body, although
it does not exercise all its functions in each part of the body -- it
is present totalitate essentiae, but not totalitate
virtutis.  But, though the soul is one, it has several
faculties, or immediate principles of action. In the Summa
Theologica  the necessity of admitting the existence of faculties
of the soul is proved by metaphysical reasons; in De Spiritualibus
Creaturis  the same conclusion is reached from considerations of a
psychological nature. The faculties of the soul are (1)
locomotive; (2) vegetative, or nutritive; (3)
(cognitive) sensitive; (4) (cognitive) intellectual; and
(5) appetitive, which includes sensitive appetite and rational
appetite, or will. This division is expressly attributed to
 Sum. Theol., Ia, LXXVI, 4, c.
 Cf. op. cit., Ia, LXXVI, 6, 7.
 Op. cit., Ia, LXXVI, 8.
All the faculties of the soul are vital, and their operations are
immanent. Some, however, are wholly dependent on states of the
organism, while others are immaterial, that is, independent of bodily
states, or, more generally, of all the conditions of matter. To this
class belong the intellectual faculties. St. Thomas, it is true, admits
that, as Aristotle taught, there is nothing in the intellect which did
not come through the senses; nevertheless he maintains, and in this he
is true to Aristotelian principles, that there is an essential
distinction between sense and intellect. The intellect is
 Ia, LXXVII, 1.
 Art. 11.
 Sum. Theol., Ia, LXX VIII, 1.
(a) Because we can know incorporeal things:
Nihil agit nisi secundum suam speciem, eo quod forma est principium
agendi in unoquoque. Si igitur intellectus sit corpus, actio ejus
ordinem corporum non excedet. Non igitur intelliget nisi corpora. Hoc
autem patet esse falsum: intelligimus enim multa quae non sunt corpora.
Intellectus igitur non est corpus. 
 C. G., II, 49.
(b) Because of our power of reflection:
Nullius corporis actio reflectitur supra agentem. Intellectus autem
supra seipsum agendo reflectit. Intelligit autem seipsum non solum
secundum partem, sed secundum totum. Non est igitur corpus. 
(c) Because of the universality and necessity which the idea possesses:
Propria operatio hominis, in quantum hujusmodi, est intelligere: per
hanc enim differt a brutis. Intelligere autem est universalium et
incorruptibilium, in quantum hujusmodi. 
 Op. cit., II, 79; cf. also Sum. Theol., Ia,
The intellect, although immaterial and therefore intrinsically
independent of the body, depends on the body extrinsically and,
as it were, accidentally; for the soul, being the weakest and most
imperfect of spiritual substances, being, in fact, substantially
incomplete without the body, cannot exercise its intellectual functions
without the cooperation of the bodily senses. Having no innate ideas,
it must obtain the matter of thought from
the world outside; the senses are, therefore, the channels of
communication between the soul and the objects of knowledge. This
extrinsic, or accidental, dependence of intellect upon sense explains
the phenomenon of mental fatigue:
Si vero in intelligendo fatigetur corpus, hoc est per accidens, in
quantum intellectus indiget operatione virium sensitivarum, per quas ei
phantasmata praeparentur. 
 Sum. Theol., Ia, LXXV, 3, ad
Intellect, therefore, while it transcends the world of sense, is
accompanied in all its operations by bodily states, to which the
operations of the intellect are correlated. St. Thomas is as careful to
avoid the ultra-spiritualism of those who deny all interaction or
correlation between the acts of the intellect and the organism, as he
is to avoid the materialism of those who make the acts of the intellect
depend intrinsically on material conditions. His doctrine on this
point, while it in no way compromises the spiritual and immaterial
nature of the principle of pure thought, leaves full scope to empirical
psychology and to psychophysical investigation.
From the distinction between intellect and sense, St. Thomas infers the
conclusion that the soul is immaterial. It is a principle of
Scholastic philosophy that action is, so to speak, a measure of
existence: agere sequitur esse. The effect cannot be greater
than the sum of its causes: if, therefore, the intellect, in the
processes of pure thought, transcends all material conditions, it
follows that the soul, which is the radical principle of such
processes, is itself immaterial.
Sic igitur ex operatione animae humanae modus esse ipsius cognosci
potest. In quantum enim habet operationem materialia transcendentem,
esse suum est supra corpus elevatum, non dependens ab eo.
 Q. Disp. De An., Art. 1.
The immortality of the soul  follows from its immateriality.
The proofs of immortality, although differently enunciated in
different portions of the writings of St. Thomas, may be said to
converge on one line of argument: the soul is immaterial; therefore it
is naturally incorruptible. For instance, in the Quaestio Disputata
De Anima  St. Thomas argues that a compound is subject to
corruption per se by the loss of the form which gives it being,
while a form, although incorruptible per se, may be corruptible
per accidens; that is to say, it is liable to destruction if it
is merely that by which the compound is, and if it has no being
independently of the compound. Now, the soul is a form, and therefore
it is not corruptible per se. It is a form independent of the
body as to its highest operations, and therefore it is independent of
the body as to its being; consequently it is not corruptible per
accidens. Therefore neither per se nor per accidens
is the soul subject to corruption. Towards the end of the article in
which the foregoing argument is enunciated, St. Thomas shows that all
who denied the natural immortality of the soul did so either (1)
because they held that the soul is a material substance; or (2) because
they held that the soul is intrinsically dependent on matter even in
its intellectual operations; or (3) because they held that the
principle of intellectual knowledge is not a faculty of the individual
soul, but something separate (intellectus separatus), which is
immortal, while the individual soul is corruptible. The argument is
repeated in Contra Gentiles, II, 55; in II, 79, of the same
work, the form of the argument is slightly changed:  the soul is
perfected by knowledge and virtue. Now, all knowledge and all virtue
are conditioned by a certain degree of separation from matter: every
idea that we acquire, every act of virtue that we
perform, lifts us above the material conditions of life and adds to
the perfection of the soul. Death, therefore, which is a complete
separation of the soul from matter, perfects rather than destroys the
 Cf. Cath. Univ. Bull. (April, 1900), Vol. VI, pp.
Arguing from the same empirical principles, -- principles, namely,
which are founded on a study of the operations of the mind, -- St.
Thomas concludes that the soul is created. If the soul, in its
intellectual acts, rises above the conditions of matter, it is
impossible that the soul could be produced by material forces: matter
cannot produce an immaterial effect. For the same reason -- because of
its immateriality -- the soul cannot by any agency be evolved out of
the potency of matter. It follows that it is created.  At the moment
of creation the soul is infused into the body: "Creando infunditur et
infundendo creatur," is the Scholastic formula. The soul is naturally
destined for the body; there is, consequently, no reason why it should
exist before its union with the body, as Plato taught.
 Art. 14.
 "Nulla res corrumpitur ex eo in quo consistit propria sua perfectio.
Perfectia autem animae consistit in quadam abstractione a corpore:
perficitur enim anima scientia et virtute: secundum scientiam autem
tanto magis perficitur quanta magis immaterialia considerat; virtutis
autem perfectia consistit in hoc quod homo corporis passiones non
sequatur sed eas secundum rationem temperet et refrenet. Non ergo
corruptio animae consistit in hoc quad a corpore separetur."
 Cf. Sum. Theol., Ia, CXVIII, 2, C; C. G., II,
It will be perceived that St. Thomas' system of rational psychology is
based on experience. The central doctrine of this system -- the
substantial union of soul and body in man -- is inferred from the facts
of consciousness, revealing to us the oneness of the vital principle
from which proceed not merely our intellectual actions, but also every
other function of the living organism. It is from the facts of
consciousness that the nature of the idea is determined, and from the
universality and necessity of the idea are deduced in turn the
immateriality and immortality of the soul, as well as the creationist
hypothesis of the origin of the soul. The method of St. Thomas'
psychology is, therefore, empirical, and not, as is too frequently
alleged, a priori. It is true that St. Thomas appeals to such
maxims and formulas as "Agere sequitur esse." But it should be
remembered that such formulas are not a priori principles or
premises arbitrarily assumed; they are conclusions established by
empirical or rational investigation, and, as such, are perfectly legitimate
principles of rational psychology -- in the same way as the law of the
conservation of energy, the law of the division of physiological labor,
or any other generalization inductively established, has its legitimate
application in physics or biology.
Genesis of knowledge. St. Thomas teaches that there are no
innate ideas: that the mind is at first a tabula rasa, pure
potency in the intellectual order, just as materia prima is pure
potency in the physical order. All knowledge begins with
sense-knowledge: "Nihil est in intellectu quod prius non fuerit in
sensu." Thus, for example, he says: 
 Sum. Theol., Ia, LXXXIV, 3.
Deficiente aliquo sensu, deficit scientia eorum quae apprehenduntur
secundum ilium sensum; sicut caecus natus nullam potest habere notitiam
The intellect, it is true, knows itself by its own act, but the act of
the intellect presupposes the previous exercise of the senses. 
 Cf. op. cit., Ia, LXXXVII, 1.
St. Thomas does not discuss in detail the nature of sensation, nor the
manner and mechanism of the process of sense-perception. He simply
describes in a general way the conditions of sense-knowledge and the
action of the object on the senses. Sensation, he teaches, is the act
by which the object produces a modification in the animated organism.
The senses, therefore, are purely passive or, at most, reactive; they
do not produce anything; they neither make the object nor do they, as
modern theories of apperception maintain, group together the qualities
of the object and unify them. The object acts; the senses react:
"Sensus non est virtus activa sed passiva . . . sensus autem comparatur
ad sensibile sicut patiens ad agens, eo quod sensibile transmutat
sensum."  The reaction is described as follows:
Sentire, quantum ad ipsam receptionem speciei sensibilis, nominat
passionem . . . sed, quantum ad actum consequentem ipsum sensum perfectum
per speciem, nominat operationem. 
 Q. Disp. De Ver., XXVI, 3, ad
Confining our attention to the passive phase of sensation, we next
inquire, What is the nature of the change produced by the object in
the organism? It is neither wholly material nor wholly immaterial;
it is a vital change. It is not entirely material, because color, for
example, is not received in the eye in such a way as to color the eye;
neither is the change purely immaterial, because we are speaking of the
modification of material organs by material qualities. When, therefore,
St. Thomas uses the phrase immutatio spiritualis  to designate the
change produced in the organs of sense-perception, he uses it as
opposed to immutatio naturalis, or wholly material change. This
"spiritual" change is the famous species sensibilis, which is
consequently nothing but a passio, or affectio, of the
peripheral sense-organs, a mode of motion, and by no means a
substantial entity. Now, according to a metaphysical principle well
known to St. Thomas as a Peripatetic formula, actio and
passio are but two phases of the same reality, like the concave
and the convex of the same curve.  The action of the object and the
modification produced by it in the sense are one and the same
phenomenon, and the species sensibilis may therefore be defined
as the physical determinant of sensation, inasmuch as it is received
in the animated organism. The species sensibilis is not a
miniature object; neither is it something which we first perceive in
sensation, and by means of which we are led to perceive the object. It
is merely the vital phase of the stimulative action of the external
object, -- a medium of communication between object and subject, but
not a medium in the order of knowledge; for in normal conditions it
does not rise into direct consciousness at all, the first thing
perceived being the object itself. It is called a species because by
means of it (in the sense just explained) the object is perceived.
 In Ium Sent., Dist. LX, I, 1, ad
 Sum. Theol., Ia, LXXVIII, 3, c.
This detailed explanation of the Thomistic doctrine of species
sensibilis is rendered necessary by the persistent
misrepresentation of that theory on the part of many writers on
Scholastic psychology.  The misunderstanding is perhaps to be
explained by the fact that St. Thomas has little to say about the
species sensibilis. In the Summa Theologica  he merely
points out the difference between the Aristotelian doctrine of
species and the atomistic doctrine of effluxes, and adds that
the species is a mode of motion:
 For instance, in In IIIum De An.,
Lect. 2, St. Thomas writes: "Sicut dictum est in tertio Physicorum quod
actio et passio sunt unus actus, subjecto, sed differunt, ratione,
prout actio signatur ut ab agente, passio autem ut in patiente."
Operationes sensitivae partis causantur per impressionem sensibilium in
sensum, non per modum defluxionis, ut Democritus posuit, sed per
 Cf, for instance, Reid, Works, p. 267.
St. Thomas does not attempt to explain in what this operatio --
this mode of motion, or as we should call it, vibration -- consists.
 Ia, LXXXIV, 6, c.
Returning now to the study of the active phase of the process of
sensation, we find that according to St. Thomas, the species is first
impressed on the sense (species impressa); then consciousness
responds and by the actus consequens impressionem writes out, so
to speak, a representation of the object, called the species
expressa. Sensation in the passive phase is not knowledge; for
there is no knowledge without consciousness: it is only in the active
phase that sensation becomes knowledge properly so called. 
 Cf. In Ium Sent., Dist.
XL, I, 1, ad 1um.
But how do we rise from sense-knowledge to intellectual
knowledge? how do we derive from the world of material things the
universal and immaterial, which is the object of pure thought? St.
Thomas recalls, in his answer to this question, the Aristotelian
distinction between active and passive intellect. These, he maintains,
are two faculties, not one and the same power viewed under two
different aspects.  The object as it presents itself to the senses is
indeed contingent and singular; but, hidden beneath the surface qualities, which give to the object its
individuality and contingency, is the unalterable nature, or essence,
which is universal and necessary. The active intellect, by
virtue of its illuminative power, separates what is contingent and
particular from what is necessary and universal in the object, in this
way causing the universal and necessary element in the object to stand
forth in the clear light of its own intelligibility, and rendering
actually intelligible what was only potentially intelligible before.
The actually intelligible element acts upon the passive, or receptive,
intellect in the same way as color acts upon the eye, producing the
species intelligibilis impressa; on being received into
intellectual consciousness, this impression becomes the intellectual
expression of the object in the mind, the mental image of the object
(species intelligibilis expressa, verbum mentis).  The idea
which results from this abstractive process has a twofold aspect:
entitatively considered, it is an accident or quality of the mind in
which it is; representatively considered, it is an image, or
representation, of the object, functioning, not as a medium in which we
see the object, -- for that would be to open the door to subjectivism,
-- but as a medium by which the object acts on our consciousness. The
analogy between the function of the species intelligibilis and
that of the species sensibilis is perfect 
 Cf. Sum. Theol., Ia, LXXIX, 7, and In
IIum Sent., Dist. XVII, Q. II, Art. 1.
With regard to the chronological order of the genesis of our
ideas, St. Thomas holds that the first idea which the human mind
acquires is the idea, or notion, of Being. By the notion of Being we
must not understand a definite concept, such as the idea of Being which
is the object of metaphysical analysis, but a vague concept of reality
more aptly expressed by the word thing than by the word
Being. St. Thomas adopts Avicenna's formula: "Quod primum cadit
in intellectu est ens." It is only after a long process of training
that the mind, by reflecting on its own acts, comes to know itself. The senses, the natural windows
of the soul, are open on the side which looks out on the external
world; consequently, our first knowledge is sense-knowledge, and the
first idea which we glean from sense-knowledge is naturally the most
imperfect, that is, the vaguest and least definite of notions, -- the
idea of Being. 
 Cf. C. G., II, 73; Sum. Theol., Ia, LXXXV, 1;
Q. Disp. De Ver., IV, 2.
 Cf. Sum. Theol., Ia, LXXXV, 2; Philosophical
Review, November, 1903.
 Op. cit., Ia, LXXXV, 3.
Ontologists have endeavored to cite the authority of St. Thomas in
favor of their doctrine that (1) God is the first object of our
knowledge, and (2) in this knowledge of God we know all things else.
St. Thomas, it need hardly be said, is far from confounding with the
idea of God the idea of Being in general, which is the first object of
knowledge, and the constant substratum and indefinite residuum in all
our processes of ideation. He is careful to keep apart the concept of
Being and the concept of God; for the former is merely an abstraction
of the mind, existing as such nowhere except in the mind, and the
latter is the representation of the first and greatest reality. When,
therefore, he says, "(Entis) intellectus includitur in omnibus
quaecumque quis apprehendit,"  he is speaking of the idea of Being
which ia the substratum of all our ideational processes, and when he
says that we see all things in God, he explains his meaning as
Omnia dicimur in Deo videre et secundum Ipsum omnia judicare, in
quantum per participationem Sui luminis omnia cognoscimus et
dijudicamus, sicut etiam omnia sensibilia dicimur videre et judicare in
sole, id est per lumen solis. Sicut ergo ad videndum aliquid
sensibiliter non est necesse quod videatur substantia solis, ita ad
videndum aliquid intelligibiliter non est necessarium quod videatur
essentia Dei. 
 Op. cit., Ia IIae, XCIV, 2, c.
The emotions are treated by St. Thomas under the name
passiones, by which word, following St. Augustine, he translates
the Greek word pathê. It may seem strange to us that the
schoolmen should treat of the emotions in connection with appetite
and will, refusing, apparently, to recognize the importance of the
emotions as mental states deserving to be coordinated with cognitive
and volitional states in a classification of mental phenomena. Still,
when we examine the nature of the emotions, we shall realize that they
are intimately connected with volitional or appetitive states -- that
all emotion is, in a certain sense, a response to good or evil
 Op. cit., Ia, XII, 11, ad 3um;
cf. Piat, Quid Divini etc. (Paris, 1890).
St. Thomas defines passion in its broadest sense as the change from a
state to its contrary, or, more strictly, from a more perfect to a less
perfect state.  The soul, being incorporeal, has no contrary states;
still, by reason of the body it can pass from a more perfect to a less
perfect state, and may be said by reason of the body to have contrary
states.  All the passions belong to the sensitive appetite, and are
divided into two great classes, passiones concupiscibiles and
passiones irascibiles, according as they belong to the
concupiscible appetite, which has for object the good or evil as
agreeable or repugnant in itself, or to the irascible appetite, which
has for object the good apprehended as subject to some circumstance of
difficulty or danger.  The emotions of the higher, or more spiritual,
kind, that is, those which belong to the intellectual appetite, are not
passions properly so called, because they do not imply a
transmutatio corporalis. 
 Cf. Q. Disp. De Ver., XXVI, 1.
Will is the faculty which has for its object the good
apprehended by reason. Appetite is concerned with the good, just as
cognition is concerned with the true. Cognition goes before
appetite, and the nature of the latter depends on the nature of the
former: sensuous appetite, the tendency towards what is good for the
body, follows sense-perception; rational appetite, or will, the
tendency towards the rational good, follows intellectual knowledge. As
the intellect cannot but assent to first principles, so the will cannot
but tend towards good in general, bonum
commune. With regard, therefore, to good in general, there is no
freedom of choice.  Choice is possible only in reference to
particular goods. Now, the intellect presents a particular good in
such a manner that, while we perceive it to be good, we perceive
at the same time, that, without it, good in general, or universal
good, may be attained. This perception is the ground of freedom.
The root of freedom (radix libertatis) is, therefore, the
reason, and freedom of choice (liberunt arbitrium) may be said
to include the action of the intellect as well as that of the will.
"Pro tanto necesse est quod homo sit liberi arbitrii ex hoc ipso
quod rationalis est." 
 Sum. Theol. Ia IIae, XXII, 1.
 Cf. Q. Disp. De Ver., XXVI, 4 and 5.
 Sum. Theol. Ia IIae, XXII, 2, ad 3um.
 Op. cit., Ia, LXXXII, 1, c.
Comparing intellect and will, St. Thomas decides that, absolutely
speaking, intellect is superior to will; although if we consider that
the object of will perfects the will, and that some of the objects of
will are superior to the object of intellect, we must, he says, decide
that in this respect (secundum quid) will is superior to
 Op. cit., Ia, LXXXIII, 1, c.
Melior est amor Dei quam cognitio; e contrario autem, melior est
cognitio rerum corporalium quam amor. Simpliciter tamen, intellectus
est nobilior quam voluntas. 
 Op. cit., Ia, LXXXII, 3, c.
4. Cosmology. The eternity of the world is not contrary to
reason, in this sense, that, absolutely speaking, God could have
created something, ab aeterno; and therefore the origin of the
world in time is not a truth demonstrable by reason.  The world, as
it exists, is good. Its goodness is apparent if we consider the end for
which it was created. It is not, however, the most perfect world
possible; for God in His infinite power could and can create a more
perfect world.  The world was created out of nothing. For all finite
being, whether potential or actual, is dependent on God. Even eternal
matter, if it existed before the production of the first forms of
actual being, must have originated by virtue of the Divine Will. "Creatio est
emanatio totius esse ex non ente, quod est nihil." 
 Op. cit., Ia, XLVI; cf. Quodl., III, Art.
Every created being is composed, as we shall see, of potency and
actuality. Everything in the visible universe is composed of matter and
form. Matter is potency; materia prima is utter indetermination,
-- potentiality and nothing more. It is described as "ingenerabilis et
incorruptibilis; una, unitate ordinis tantum." And, again: "omnium
generabilium et corruptibilium est eadem materia. . . . Est sua
potentia passiva, sicut Deus est potentia activa."  Form confers
actuality and specific determination: "Forma, secundum id quod est,
actus est, et per eam res actu existunt."  Form is the principle of
action and being: in living things it is the principle of life, and in
all material things it is the source of all qualities, even of
impenetrability and extension. It is important, in view of modern
theories of matter, to note that according to the schoolmen the actual
extension of a body is due to the form, although the potency of
extension comes from the matter. It is because matter contains the
potency of extension that St. Thomas says, "Quantitas se tenet ex parte
 Q. Disp. De Ver., XXIII, 4.
 Sum. Theol., II, XLV, I, c.
 Cf. op. cit., Ia, LXVI.
The form is the source of all actuality in material substances; it is
the determining principle, causing the substance to be what it is: it
is, therefore, the principle of specific distinction. The principle of
individuation, namely, that by which individuals of the same species
are differentiated, is matter, -- not matter in general, for that
enters into the specific definition, and is common to all members of
the species, but matter terminated by its dimensions, "Materia
determinatis dimensionibus signata." [88a] It
follows from this (and St. Thomas admits the inference) that, since
the angelic nature is form without matter, there is no numerical
distinction among spiritual substances: "Sequitur quod impossibile sit
esse duos angelos unius speciei."  "Quot sunt individua, tot sunt
species."  The human soul is like the angelic nature inasmuch as it is
spiritual, but unlike it inasmuch as it is the substantial form of the
body. It is individuated by the body, and after its separation from the
body each soul still retains a certain habitudo ad corpus which
distinguishes it from other human souls. 
 C. G., II, 30.
 In IVum Sent., Dist. XII, I,
[88a] Cf. In IIIum De An., Lect.
8: "In omnibus habentibus formam in materia non est omnino idem et res
et quod quid est ejus . . . . Manifestum est enim quod quantitas
immediate inhaeret substantiae; qualitates autem sensibiles in
quantitate fundantur. Quaedam ergo sunt formae quae materiam requirunt
sub determinata dispositione sensibilium qualitatum; et hujusmodi sunt
omnes formae naturales." Cf. also De Ente et Essentia,
The principle, "Omne quod movetur, quantum ad aliquid manet et quantum
ad aliquid transit,"  is the basis of the Thomistic as it was of the
Aristotelian doctrine of matter and form. Both St. Thomas and Aristotle
assumed that there are substantial changes, and, in order to explain
substantial change, they postulated the existence of two substantial
principles, the one (matter) permanent and the other
[88b] Sum. Theol., Ia, L. 4, c.
 De Ente et Ess., Cap. 5.
 Cf. Sum. Theol., Ia, LXXVI; Q. Disp. De An.,
Art. 20; De Spir. Creat., 2, 8.
 Sum. Theol., Ia, IX, 1.
Space, although real, is not something distinct from the
dimensions of existing bodies; it is not infinite, for it is
coterminous with the limits of the actual universe, beyond which
nothing exists except potential space. 
 Cf. In IVum Physicorum,
Time. St. Thomas accepts the Aristotelian definition of time. In
the Summa Theologica  he teaches that it is the mind which
alternates the present instant, thus, as it were, constituting the
flow, or succession which is time: "Fluxus ipsius nunc, secundum quod
alternatur ratione, est tempus." And in the Commentaries on the
Books of Sentences  he quotes with approval the Aristotelian
principle, "Si non esset anima, non esset tempus."
 Ia, X, 4, ad 2um.
Neither St. Thomas nor any of his contemporaries imagined the
heavenly bodies to be composed of the same matter as that
of the physical world around us. The matter of the terrestrial world
is made up of the four elements; celestial matter is different from
terrestrial matter or is, at most, only analogous to it.  The
heavenly bodies are incorruptible, because in them the form fills all
the potency of the matter: "Illa forma sic perficit illam materiam quod
nullo modo in ea remanet potentia ad esse, sed ad ubi tantum." 
 I., Dist. XIX, II, 1.
 Sum. Theol., Ia, LXVI, 2.
5. Metaphysics and Natural Theology. Being is that which
exists or can exist either in the mind or outside the mind.  It is
opposed to Not-Being (nihil). The notion of Being is peculiar in
this, that it can neither be defined nor divided, because of the
simplicity of its comprehension and the universality of its extension.
Being is, therefore, reduced to lower classes, such as substance,
animal, man, not by adding some difference distinct from Being
itself, but by bringing out explicitly in the lower classes what is
implicitly contained in the comprehension of the notion of Being in
general. Hence, Being is not to be predicated univocally of its lower
 Ibid. According to St. Thomas, intelligences move the heavenly
spheres: "Ad hoc antem ut moveat, non oportet quod uniatur ei ut forma
sed per contactum virtutis, sicut motor unitur mobili." op. cit., Ia,
 Cf. op. cit., Ia, III, 4.
Being is the most universal of notions; it is, in fact,
transcendental, that is to say, extending above and beyond all
classes. It includes the highest reality as well as the lowest, --
God, Who is pure actuality, as well as materia prima, which is
mere potency. Between these two poles of existence range all created
beings; for in everything created there is a dual composition of
actuality and potency, actus et potentia. Even in the highest of
the angels, immaterial as he is, there is not only a composition of
essence and existence, -- of that by which he is, and the act of
existence, -- but also a composition of substance and accident. In
material things there is a threefold composition: (1) of essence
and existence; (2) of substance and accident; and (3) of matter and
form. God alone is free from all composition; in Him there is no matter
or potency of any kind: His essence is His existence, His action is His
substance, He is pure actuality, Actus Purus.  Thus does the
metaphysics of St. Thomas point heavenward not only in the ultimate
problems of the existence and nature of God, but also in its initial
concept, -- the dualism of all created being.
 C. G., I, 25; Sum. Theol., Ia, III, 5.
 Cf. op. cit., Ia, III, 4; VII, 2.
The principles of being in the ontological order (prima principia
essendi) are the four causes, -- matter, form, efficient
cause, and final cause. Each of these is, in its own way, a
cause, in so far as the effect depends on it.  The principles of
being in the logical order (prima principia cognoscendi) are
immediate analytical truths, sometimes known as axiomata or
dignitates . The first of these, the starting point of all
demonstration, is the principle of contradiction; for just as the
notion of Being is the first object of the act of ideation and that on
which all subsequent ideation is based, so the principle of
contradiction, which springs, as it were, from the first elementary
analysis of the notion of Being, is the first object of the act of
judgment and the foundation on which all our other judgments
 Op. cit., IIa IIae, XXVII, 3, c.
The highest classes of being are the categories, -- substance,
etc. St. Thomas, following Aristotle, distinguishes the first
substance, which is the individual, or hypostasis, and the
second substance, which is the universal substantial nature
abstracted from the individual. First substance really exists as such.
Second substance does not exist as such, except in the mind. It is the
quiddity, or essence, which is expressed by the definition, and which,
as thus defined, exists in the mind alone; for in concrete things it is
 In IVum Metaphysicorum, Lect. 6.
 Cf. De Ente et Ess., Cap. 4; Sum. Theol.,
Ia, XXIX, 2.
The existence of God is a truth which is per se nota quoad se.
The proposition God exists is analytical; for if we could comprehend
the subject of the proposition, we should see immediately that it
includes the predicate, -- that of itself the Divine Nature includes
existence. But we cannot adequately comprehend the subject of the
proposition. For us, therefore (quoad nos), the proposition
God exists is not self-evident or analytical. Consequently it
must be demonstrated. 
 Sum. Theol., Ia, II, I.
St. Thomas, after examining and rejecting  St. Anselm's ontological
argument, proceeds  to point out the five ways in which, by arguing
from effect to cause (a posteriori), the existence of God may be
proved. These ways are: (1) from the principles that whatever is moved
is moved by something else (quidquid movetur ab alio movetur),
and that an infinite series of moving agents is impossible (non est
procedere in infinitum); (2) from the relation between cause and
effect, -- "Non est possibile quod in causis efficientibus procedatur
in infinitum" ; (3) from the relation of the contingent to the
necessary, -- "Si omnia sunt possibilia non esse, aliquando nihil fuit
in rebus: non ergo omnia entia sunt possibilia, sed oportet aliquid
esse necessarium in rebus"; (4) from the different degrees of
perfection in things which exist, -- "Magis et minus dicuntur de
diversis, secundum quod appropinquant diversimode ad aliquid quod
maxime est"; (5) from the order and adaptation of the universe, -- "Ea
quae non habent cognitionem non tendunt in finem, nisi directa ab aliquo
cognoscente et intelligente."
 Op. cit., Ia, II, 3.
But although we can know that God exists we cannot comprehend what He
is. Not even in that unobstructed vision of the Divine Nature which
constitutes the supreme happiness of the blessed in heaven can the
human mind fully and adequately comprehend the nature of God. 
Nevertheless, even in this life we can attain an imperfect knowledge of
what God is; for we can proceed (1) by way of analogy, that is, by purifying
from all imperfection attributes which denote perfection in created
things, and predicating of God attributes thus sublimated; and (2) by
way of negation, that is, by excluding from God such attributes as
imply imperfection, and thus determining what God is not.  Proceeding
by this twofold method, St. Thomas shows that God is pure actuality
(Actus Purus); from which it follows that He is infinite,
perfect, one, immutable, eternal, etc.
 Op. cit., Ia, II, 1, ad 1um.
 Op. cit., Ia, XII, 7.
In relation to creatures, God is Creator and Preserver.
He is the first efficient cause on whom all finite being depends, --
for He made all creatures out of nothing; He is also the first exemplar
cause, because He made all things according to the ideas, or types,
which existed in the Divine Mind through all eternity. He is, moreover,
the preserver and ruler of the world; He watches over all His creatures
and conserves them; for without His sustaining hand they would return
to the nothing out of which He brought them.  He cooperates in all
our actions, in the natural as well as in the supernatural order. 
Finally, He is the ultimate end for which all things were made, and to
which all rational creatures tend to return. 
 Op. cit., Ia, XII, 12.
 Cf. op. cit., Ia, CIV, 1.
This last consideration brings us to St. Thomas' ethical doctrines.
 Op. cit., Ia, CV, 5.
 Op. cit., Ia, XLIV, 4.
6. Moral and Political Doctrines. The object of all appetite is
the good; the end of all human action is happiness. Universal good,
which is the conscious or unconscious aim of all rational action, is
fully realized in the infinite good, which is God. God alone, as St.
Augustine taught, can fill the void of the human heart; and man will
not rest until he attains the happiness which leaves no desire
unsatisfied. St. Thomas teaches that it is derogatory to the dignity of
man to seek final and ultimate happiness in anything short of the
 Op. cit., Ia IIae, 111, 8.
Although the knowledge and love of God, in which consists the enjoyment
of the infinite good, are to be fully realized only in the next life,
yet here on earth there is an imperfect form of happiness which man may
attain. "Aliqualis beatitudinis participatio in hac vita haberi potest;
perfecta autem et vera beatitudo non potest haberi in hac vita."  As
constituents of this imperfect happiness, St. Thomas mentions health,
external goods, and the society of friends. 
 Op. cit., Ia IIae, V, 3.
The moral goodness or evil of an action depends ultimately on whether
the action leads to or averts from the end for which man was created,
and proximately on the object, circumstances, and purpose of the action
 Op. cit., Ia IIae, IV, 6, 7, 8.
Omnis actio in quantum habet aliquid de esse in tantum habet de
bonitate; in quantum vero ei aliquid deficit de plenitudine essendi, in
tantum deficit a bonitate et sic dicitur mala.
If object, circumstances, and end (intention) are good, the action is
good; if any of these is evil, the action is evil. Hence the Scholastic
adage, "Bonum ex integra causa; malum ex quocumque defectu." 
 Op. cit., Ia IIae, XVIII, 1.
Virtue is defined,  "Bona qualitas mentis, qua recte vivitur,
qua nullus male utitur." The theological virtues -- faith, hope, and
charity -- are infused; natural virtues, whether intellectual or moral,
are acquired by exercise in the actions pertaining to such virtues,
although the aptitude for one virtue or another, as well as the general
aptitude for virtue, is part of the natural endowment of man.
 Op. cit., Ia IIae, LV, 4.
Virtutes in nobis sunt a natura secundum aptitudinem et inchoationem,
non autem secundum perfectionem, praeter virtutes theologicas, quae
sunt totaliter ab extrinseco. 
 Op. cit., Ia IIae, LXIII, 1.
St. Thomas follows the Aristotelian classification of
moral virtues, basing it on the division of the objects of the
Sometimes  he divides moral virtues into four principal, or
 Op. cit., Ia IIae, LX, 4.
Law is the extrinsic principle of morality. It is defined
"Quaedam ordinatio rationis, ad bonum commune ab eo qui curam
communitatis habet promulgata."  A law, therefore, in order to be
obligatory, must be reasonable; it must be for the good of the
community; it must issue from the proper authority, and it must be duly
promulgated. St. Thomas distinguishes eternal, or divine,
law; natural law, which is a participation of the divine law and is
promulgated by being written "in the fleshly tables of the heart"; and
positive law,  which is a derivation from eternal law and is
divided into divine, ecclesiastical, and civil law. 
 Op. cit., Ia IIae, LXI.
 Op. cit., Ia IIae, XC, 4.
The State. The treatise De Regimine Principis is now
universally conceded to be the work of two authors. The first two books
are undoubtedly to be ascribed to St. Thomas;  the other two were
added by some disciple, probably by Ptolemy of Lucca. In the first two
books of De Regimine Principis, in the commentaries on the
Politics of Aristotle, and elsewhere in his different works St.
Thomas expounds the following political doctrines.
 Cf. op. cit., Ia IIae, XCI.
 Cf. op. cit.. Ia IIae, XCIII ff.
 De Maria, in his edition of the Opuscula (3 vols., Rome,
1886), includes merely the first four chapters of the second book among
the genuine writings of St. Thomas. cf. Vol. II, p. 42.
(a) Man is naturally ordained for the society of his fellowmen: "Est
homini naturale quod in societate multorum vivat." 
 De Regimine Principis, I, 1.
(b) Authority in civil society must have in view the public good; if it
lose sight of this, it becomes unjust, anti-social, and
tyrannical.  Tyrannical authority is held in check by the authority
of the Church, which provides for the spiritual welfare of all the
faithful, and has the power, at least in the case
of the apostasy of the tyrant, to absolve his subjects from obedience
on the ground that the ruler is an apostate.  Besides, if the rule of a
tyrant is contrary to public good or to divine law, it ceases to bind
in conscience. 
(c) Tyrannical power is also held in check by the popular will.
Tyrannicide is to be condemned.  The redress to which the subjects of a
tyrant have a just right must be sought, not by an individual, but by
an authority temporarily constituted by the people and acting according
 "Aliquis per infidelitatem peccans potest sententialiter jus
dominji amittere sicut etiam quandoque propter alias culpas." Sum.
Theol., IIa 11ae, XII, 2.
 Op. cit., Ia IIae, XCVI, 4.
 De Reg. Princip., I, 6.
Nec putanda est talis multitudo infideliter agere tyrannum destituens
etiam si eidem in perpetuum se ante subjecerat: quia hoc ipse meruit in
multitudinis regimine se non fideliter gerens.
(d) The aim of the state is not merely economical, but also
moral; and from this principle St. Thomas deduces conclusions which are
in remarkable accordance with modern political theories -- for example,
that it is the duty of the state to provide for the education of all
its members and to see that no citizen suffers want. 
 Baumano, Staatslehre des heil. Thomas von Aquino (Leipzig,
1873), pp. 161 ff.; cf. Revue Néo-Scolastique,
1895, pp. 27 ff.; Crahay, La Politique de Saint Thomae d'Aquin
(e) St. Thomas has no predilection for one form of government
rather than another. He argues, on general grounds, that the unity of
society is better secured by the rule of jine than by the rule of the
few or of the many. Still, he maintains that the aristocratic and
democratic forms of government are as legitimate as the monarchical
form. He sets forth the advantages of a constitution in which all have
a voice in the government of the state, "Ut omnes aliquam partem
habeant in principatu: per hoc enim conservatur pax populi,"  and
he lays down the general principle that it is not the form of
government, but the fidelity with which the government adheres to
the purpose for which it is instituted, that decides the happiness and
prosperity of the subjects. 
 Sum. Theol., Ia IIae, CV, 1.
Historical Position. An organic synthesis of the elements of
thought contained in preceding systems is as real an advance in the
development of philosophy as is the introduction of elements absolutely
new. In the one as well as in the other respect, the philosophy of St.
Thomas is to be pronounced an advance in philosophic thought.
 De Reg. Princip., I, 3. On St. Thomas' economic doctrines,
cf. Rev. Néo. Scol., 1896, pp. 67, 161, 286.
St. Thomas synthesized the more or less fragmentary truths which,
during the preceding centuries, the schoolmen had slowly gathered
together, as well as the elements of thought which, during the early
part of the century in which he lived, Scholasticism had derived from
Greek and Arabian sources. He perfected the Scholastic method, and
consecrated to the service of truth the dialectic which rationalists
had abused and which mystics had denounced. He gave to the doctrine of
moderate realism its final expression, and enunciated a theory of
universals which united what is true in Platonism with what is true in
nominalism. He was the first to formulate a complete system of
Christian Aristotelianism, thus pressing into the service of orthodoxy
the philosopher to whom Arabian and Jewish unbelievers had looked as
their champion in the warfare which they waged on Christianity. He
determined for all time the true relation between faith and reason,
and, while avoiding the extremes of rationalism and mysticism, gave
permanent form to the thought which had inspired every Christian
philosopher since the days of Justin, the first of the great
apologists. And all this he accomplished not so much by creating as by
transforming and assimilating. With a comprehensiveness of purpose
which, in these modern times, seems nothing short of stupendous, he
laid broad and deep the foundations of his vast synthetic system, and
with a force and directness less easily to
be attained in the rich confusion of modern thought, compelled every
source of knowledge to yield him material for his work. He drew from
the Scriptures, from the Fathers, from the philosophers of Greece and
Rome, from his predecessors in the Christian schools, and from
contemporary Arabian and Jewish philosophers. It detracts neither from
the recognized importance of those who preceded St. Thomas, nor from
his own just title to praise as an original thinker, to say that he
perfected the work of his predecessors, and, from materials which they
supplied, reconstructed the edifice of Christian philosophy.
What is new and wholly original in the work of St. Thomas is the spirit
in which he addressed himself to his task -- the sense of completeness
which impelled him to leave nothing incomplete or imperfect except in
so far as everything human must be incomplete and imperfect; the mind
appreciative of the value of truth wheresoever truth is found, and the
belief, stronger and more deep-rooted in him than in any other
schoolman, that all truth and all knowledge, from whatever source it is
derived, is capable of harmonious adjustment.
In point of detail, St. Thomas contributed to Scholastic philosophy the
doctrines by which the Dominican tradition was distinguished from the
Franciscan teaching, -- the oneness of the substantial form in each
individual, the doctrine of subsistent forms, the denial of the
rationes seminales in the sense in which they were admitted by
St. Bonaventure, and the affirmation of the real distinction between
the soul and its faculties. It was on these points that, as we shall
see, Thomists and anti-Thomists came to be divided.
It is only when, as we study the history of later Scholasticism and the
history of the philosophy of modern times, we shall look back to the
thirteenth century through the perspective of ages of less successful
attempts at philosophical synthesis, that we shall begin to realize the
true grandeur of the most commanding figure in the history of mediaeval