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Real Time Analytics
History of Modern Philosophy
Theory of Knowledge
by Falckenberg, Richard


Locke's theory of knowledge is controlled by two tendencies, one native, furnished by the Baconian empiricism, and the other Continental, supplied by the Cartesian question concerning the origin of ideas. Bacon had demanded the closest connection with experience as the condition of fruitful inquiry. Locke supports this commendation of experience by a detailed description of the services which it renders to cognition, namely, by showing that, in simple ideas, perception supplies the material for complex ideas, and for all the cognitive work of the understanding. Descartes had divided ideas, according to their origin, into three classes: those which are self-formed, those which come from without, and those which are innate (p. 79), and had called this third class the most valuable. Locke disputes the existence of ideas in the understanding from birth, and makes it receive the elements of knowledge from the senses, that is, from without. He is a representative of sensationalism,--not in the stricter sense, first put into the term by those who subsequently continued his endeavors, that thought arises from perception, that it is transformed sensation--but in the wider sense, that thought is (free) operation with ideas, which are neither created by it nor present in it from the first, but given to it by perception, that, consequently, the cognitive process begins with sensation and so its first attitude is a passive one. From the standpoint of the Cartesian problem, which he solves in a sense opposite to Descartes, Locke supplements the empiricism of Bacon by basing it on a psychologically developed theory of knowledge. That in the course of the inquiry he introduces a new principle, which causes him to diverge from the true empirical path, will appear in the sequel.

The question "How our ideas come into the mind" receives a negative answer (in the first book of the Essay: "There are no innate principles in the mind"[1] The doctrine of the innate character of certain principles is based on their universal acceptance. The asserted agreement of mankind in regard to the laws of thought, the principles of morality, the existence of God, etc., is neither cogent as an argument nor correct in fact. In the first place, even if there were any principles which everyone assented to, this would not prove that they had been created in the soul; the fact of general consent would admit of a different explanation. Granted that no atheists existed, yet it would not necessarily follow that the universal conviction of the existence of God is innate, for it might have been gradually reached in each case through the use of the reason--might have been inferred, for instance, from the perception of the purposive character of the world. Second, the fact to which this theory of innate ideas appeals is not true. No moral rule can be cited which is respected by all nations. The idea of identity is entirely unknown to idiots and to children. If the laws of identity and contradiction were innate they must appear in consciousness prior to all other truths; but long before a child is conscious of the proposition "It is impossible for the same thing to be and not to be," it knows that sweet is not bitter, and that black is not white. The ideas first known are not general axioms and abstract concepts, but particular impressions of the senses. Would nature write so illegible a hand that the mind must wait a long time before becoming able to read what had been inscribed upon it? It is often said, however, that innate ideas and principles may be obscured and, finally, completely extinguished by habit, education, and other extrinsic circumstances. Then, if they gradually become corrupted and disappear, they must at least be discoverable in full purity where these disturbing influences have not yet acted; but it is especially vain to look for them in children and the ignorant. Perhaps, however, these possess such principles unconsciously; perhaps they are imprinted on the understanding, without being attended to? This would be a contradiction in terms. To be in the mind or the understanding simply means "to be understood" or to be known; no one can have an idea without being conscious of it. Finally, if the attempt be made to explain "originally in the mind" in so wide a sense that it would include all truths which man can ever attain or is capable of discovering by the right use of reason, this would make not only all mathematical principles, but all knowledge in general, all sciences, and all arts innate; there would be no ground even for the exclusion of wisdom and virtue. Therefore, either all ideas are innate or none are. This is an important alternative. While Locke decides for the second half of the proposition, Leibnitz defends the first by a delicate application of the concept of unconscious representation and of implicit knowledge, which his predecessor rejects out of hand.

[Footnote 1: According to Fox Bourne this first book was written after the others. Geil (Ueber die Abhängigkeit Lockes von Descartes Strassburg, 1887, chap, iii.) has endeavored to prove that, since the arguments controverted are wanting in Descartes, the attack was not aimed at Descartes and his school, but at native defenders of innate ideas, as Lord Herbert of Cherbury and the English Platonists (Cudworth, More, Parker, Gale). That along with these the Cartesian doctrine was a second and chief object of attack is shown by Benno Erdmann in his discussion of the treatises by G. Geil and R. Sommer (Lockes Verhältnis zu Descartes Berlin, 1887) in the Archiv für Geschichte der Philosophie ii, pp. 99-121.]

Locke's positive answer to the question concerning the origin of ideas is given in his second book. Ideas are not present in the understanding from the beginning, nor are they originated by the understanding, but received through sensation. The understanding is like a piece of white paper on which perception inscribes its characters. All knowledge arises in experience. This is of two kinds, derived either from the external senses or the internal sense. The perception of external objects is termed Sensation, that of internal phenomena (of the states of the mind itself) Reflection. External and internal perception are the only windows through which the light of ideas penetrates into the dark chamber of the understanding. The two are not opened simultaneously, however, but one after the other; since the perceptions of the sensible qualities of bodies, unlike that of the operations of the mind itself, do not require an effort of attention, they are the earlier. The child receives ideas of sensation before those of reflection; internal perception presupposes external perception.

In this distinction between sensation and reflection, we may recognize an after-effect of the Cartesian dualism between matter and spirit. The antithesis of substances has become a duality in the faculties of perception. But while Descartes had so far forth ascribed precedence to the mind in that he held the self-certitude of the ego to be the highest and clearest of all truths and the soul to be better known than the body, in Locke the relation of the two was reversed, since he made the perception of self dependent on the precedent perception of external objects. This antithesis was made still sharper in later thinking, when Condillac made full use of the priority of sensation, which in Locke had remained without much effect; while Berkeley, on the other hand, reduced external perception to internal perception.

All original ideas are representations either of the external senses or of the internal sense, or of both. And since, in the case of ideas of sensation, there is a distinction between those which are perceived by a single one of the external senses and those which come from more than one, four classes of simple ideas result: (1) Those which come from one external sense, as colors, sounds, tastes, odors, heat, solidity, and the like. (2) Those which come from more than one external sense (sight and touch), as extension, figure, and motion. (3) Reflection on the operations of our minds yields ideas of perception or thinking (with its various modes, remembrance, judging, knowledge, faith, etc.), and of volition or willing. (4) From both external and internal perception there come into the mind the ideas of pleasure and pain, existence, power, unity, and succession. These are approximately our original ideas, which are related to knowledge as the letters to written discourse; as all Homer is composed out of only twenty-four letters, so these few simple ideas constitute all the material of knowledge. The mind can neither have more nor other simple ideas than those which are furnished to it by these two sources of experience.

Locke differs from Descartes again in regard to extension and thought. Extension does not constitute the essence of matter, nor thought the essence of mind. Extension and body are not the same; the former is presupposed by the latter as its necessary condition, but it is the former alone which yields mathematical matter. The essence of physical matter consists rather in solidity: where impenetrability is found there is body, and the converse; the two are absolutely inseparable. With space the case is different. I cannot conceive unextended matter, indeed, but I can easily conceive immaterial extension, an unfilled space Further, if the essence of the soul consisted in thought, it must be always thinking. As the Cartesians maintained, it must have ideas as soon as it begins to be, which is manifestly contrary to experience. Thinking is merely an activity of the mind, as motion is an activity of the body, and not its essential characteristic. The mind does not receive ideas until external objects occasion perception in it through impressions, which it is not able to avert. The understanding may be compared to a mirror, which, without independent activity and without being consulted, takes up the images of things. Some of the simple ideas which have been mentioned above represent the properties of things as they really are, others not. The former class includes all ideas of reflection (for we are ourselves the immediate object of the inner sense); but among the ideas of sensation those only which come from different senses, hence extension, motion and rest, number, figure, and, further, solidity, are to be accounted primaryqualities, i. e, such as are actual copies of the properties of bodies. All other ideas, on the contrary, have no resemblance to properties of bodies; they represent merely the ways in which things act, and are not copies of things. The ideas of secondary or derivative qualities (hard and soft, warm and cold, colors and sounds, tastes and odors) are in the last analysis caused--as are the primary--by motion, but not perceived as such. Yellow and warm are merely sensations in us, which we erroneously ascribe to objects; with equal right we might ascribe to fire, as qualities inherent in it, the changes in form and color which it produces in wax and the pain which it causes in the finger brought into proximity with it. The warmth and the brightness of the blaze, the redness, the pleasant taste, and the aromatic odor of the strawberry, exist in these bodies merely as the power to produce such sensations in us by stimulation of the skin, the eye, the palate, and the nose. If we remove the perceptions of them, they disappear as such, and their causes alone remain--the bulk, figure, number, texture, and motion of the insensible particles. The ground of the illusion lies in the fact that such qualities as color, etc., bear no resemblance to their causes, in no wise point to these, and in themselves contain naught of bulk, density, figure, and motion, and that our senses are too weak to discover the material particles and their primary qualities.--The distinction between qualities of the first and second order--first advanced by the ancient atomists, revived by Galileo and Descartes on the threshold of the modern period, retained by Locke, and still customary in the natural science of the day--forms an important link in the transition from the popular view of all sense-qualities as properties of things in themselves to Kant's position, that spatial and temporal qualities also belong to phenomena alone, and are based merely on man's subjective mode of apprehension, while the real properties of things in themselves are unknowable.

Thus far the procedure of the understanding has been purely passive. But besides the capacity for passively receiving simple ideas, it possesses the further power of variously combining and extending these original ideas which have come into it from without, of working over the material given in sensation by the combination, relation, and separation of its various elements. In this it is active, but not creative. It is not able to form new simple ideas (and just as little to destroy such as already exist), but only freely to combine the elements furnished without its assistance by perception (or, following the figure mentioned above, to combine into syllables and words the separate letters of sensation). Complex ideas arise from simple ideas through voluntary combination of the latter.

Perception is the first step toward knowledge. After perception the most indispensable faculty is retention, the prolonged consciousness of present ideas and the revival of those which have disappeared, or, as it were, have been put aside. For an idea to be "in the memory" means that the mind has the capacity to reproduce it at will, whereupon it recognizes it as previously experienced. If our ideas are not freshened up from time to time by new impressions of the same sort they gradually fade out, until finally (as the idea of color in one become blind in early life) they completely disappear. Ideas impressed upon the mind by frequent repetition are rarely entirely lost. Memory is the basis for the intellectual functions of discernment and comparison, of composition, abstraction, and naming. Since, amid the innumerable multitude of ideas, it is not possible to assign to each one a definite sign, the indispensable condition of language is found in the power of abstraction, that is, in the power of generalizing ideas, of compounding many ideas into one, and of indicating by the names of the general ideas, or of the classes and species, the particular ideas also which are contained under these. Here is the great distinction between man and the brute. The brute lacks language because he lacks (not all understanding whatever, e.g. not a capacity, though an imperfect one, of comparison and composition, but) the faculty of abstraction and of forming general ideas. The object of language is simply the quick and easy communication of our thoughts to others, not to give expression to the real essence of objects. Words are not names for particular things, but signs of general ideas; and abstracta nothing more than an artifice for facilitating intellectual intercourse. This abbreviation, which aids in the exchange of ideas, involves the danger that the creations of the mind denoted by words will be taken for images of real general essences, of which, in fact, there are none in existence, but only particular things. In order to prevent anyone to whom I am speaking from understanding my words in a different sense from the one intended, it is necessary for me to define the complex ideas by analyzing them into their elements, and, on the other hand, to give examples in experience of the simple ideas, which do not admit of definition, or to explain them by synonyms. Thus much from Locke's philosophy of language, to which he devotes the third book of the Essay

Complex ideas, which are very numerous, may be divided into three classes: Modes, Substances, and Relations.

Modes(states, conditions) are such combinations of simple ideas which do not "contain in them the supposition of subsisting by themselves, but are considered as dependencies on, or affections of substances." They fall into two classes according as they are composed of the same simple ideas, or simple ideas of various kinds; the former are called simple, the latter mixed, modes. Under the former class belong, for example, a dozen or a score, the idea of which is composed of simple units; under the latter, running, fighting, obstinacy, printing, theft, parricide. The formation of mixed modes is greatly influenced by national customs. Very complicated transactions (sacrilege, triumph, ostracism), if often considered and discussed, receive for the sake of brevity comprehensive names, which cannot be rendered by a single expression in the language of other nations among whom the custom in question is not found. The elements most frequently employed in the formation of mixed modes are ideas of the two fundamental activities, thinking and motion, together with power, which is their source. Locke discusses simple modes in more detail, especially those derived from the ideas of space, time, unity, and power. Modifications of space are distance, figure, place, length; since any length or measure of space can be repeated to infinity, we reach the idea of immensity. As modes of time are enumerated succession (which we perceive and measure only by the flow of our ideas), duration, and lengths or measures of duration, the endless repetition of which yields the idea of eternity. From unity are developed the modes of numbers, and from the unlimitedness of these the idea of infinity. No idea, however, is richer in modes than the idea of power. A distinction must be made between active power and passive power, or mere receptivity. While bodies are not capable of originating motion, but only of communicating motion received, we notice in ourselves, as spiritual beings, the capacity of originating actions and motions. The body possesses only the passive power of being moved, the mind the active power of producing motion. This latter is termed "will." Here Locke discusses at length the freedom of the will, but not with entire clearness and freedom from contradictions (cf. below).

Modes are conditions which do not subsist of themselves, but have need of a basis or support; they are not conceivable apart from a thing whose properties or states they are. We notice that certain qualities always appear together, and habitually refer them to a substratum as the ground of their unity; in which they subsist or from which they proceed. Substance denotes this self-existent "we know not what," which has or bears the attributes in itself, and which arouses the ideas of them in us. It is the combination of a number of simple ideas which are presumed to belong to one thing. From the ideas of sensation the understanding composes the idea of body, and from the ideas of reflection that of mind. Each of these is just as clear and just as obscure as the other; of each we know only its effects and its sensuous properties; its essence is for us entirely unknowable. Instead of the customary names, material and immaterial substances, Locke recommends cogitative and incogitative substances, since it is not inconceivable that the Creator may have endowed some material beings with the capacity of thought. God,--the idea of whom is attained by uniting the ideas of existence, power, might, knowledge, and happiness with that of infinity,--is absolutely immaterial, because not passive, while finite spirits (which are both active and passive) are perhaps only bodies which possess the power of thinking.

While the ideas of substances are referred to a reality without the mind as their archetype, to which they are to conform and which they should image and represent, Relations(e.g. husband, greater) are free and immanent products of the understanding. They are not copies of real things, but represent themselves alone, are their own archetypes. We do not ask whether they agree with things, but, conversely, whether things agree with them (Book iv. 4.5). The mind reaches an idea of relation by placing two things side by side and comparing them. If it perceives that a thing, or a quality, or an idea begins to exist through the operation of some other thing, it derives from this the idea of the causal relation, which is the most comprehensive of all relations, since all that is actual or possible can be brought under it. Cause is that which makes another thing to begin to be; effect that which had its beginning from some other thing. The production of a new quality is termed alteration; of artificial things, making; of a living being, generation; of a new particle of matter, creation. Next in importance is the relation of identity and diversity Since it is impossible for a thing to be in two different places at the same time and for two things to be at the same time in the same place, everything that at a given instant is in a given place is identical with itself, and, on the other hand, distinct from everything else (no matter how great the resemblance between them) that at the same moment exists in another place. Space and time therefore form the principium individuationis By what marks, however, may we recognize the identity of an individual at different times and in different places? The identity of inorganic matter depends on the continuity of the mass of atoms which compose it; that of living beings upon the permanent organization of their parts (different bodies are united into one Animal by a common life); personal identity consists in the unity of self-consciousness, not in the continuity of bodily existence (which is at once excluded by the change of matter). The identity of the person or the ego must be carefully distinguished from that of substance and of man. It would not be impossible for the person to remain the same in a change of substances, in so far as the different beings (for instance, the souls of Epicurus and Gassendi) participated in the same self-consciousness; and, conversely, for a spirit to appear in two persons by losing the consciousness of its previous existence. Consciousness is the sole condition of the self, or personal identity.--The determinations of space and time are for the most part relations. Our answers to the questions "When?" "How long?" "How large?" denote the distance of one point of time from another (e.g. the birth of Christ), the relation of one duration to another (of a revolution of the sun), the relation of one extension to another well-known one taken as a standard. Many apparently positive ideas and words, as young and old, large and small, weak and strong, are in fact relative. They imply merely the relation of a given duration of life, of a given size and strength, to that which has been adopted as a standard for the class of things in question. A man of twenty is called young, but a horse of like age, old; and neither of these measures of time applies to stars or diamonds. Moral relations, which are based on a comparison of man's voluntary actions with one of the three moral laws, will be discussed below.

The inquiry now turns from the origin of ideas to their cognitive value or their validity beginning (in the concluding chapters of the second book) with the accuracy of single ideas, and advancing (in Book iv., which is the most important in the whole work) to the truth of judgments. An idea is real when it conforms to its archetype, whether this is a thing, real or possible, or an idea of some other thing; it is adequate when the conformity is complete. The idea of a four-sided triangle or of brave cowardice is unreal or fantastical, since it is composed of incompatible elements, and the idea of a centaur, since it unites simple ideas in a way in which they do not occur in nature. The layman's ideas of law or of chemical substances are real, but inadequate, since they have a general resemblance to those of experts, and a basis in reality, but yet only imperfectly represent their archetypes. Nay, further, our ideas of substances are all inadequate, not only when they are taken for representations of the inner essences of things (since we do not know these essences), but also when they are considered merely as collections of qualities. The copy never includes all the qualities of the thing, the less so since the majority of these are powers, i.e. consist in relations to other objects, and since it is impossible, even in the case of a single body, to discover all the changes which it is fitted to impart to, or to receive from, other substances. Ideas of modes and relations are all adequate, for they are their own archetypes, are not intended to represent anything other than themselves, are images without originals. An idea of this kind, however, though perfect when originally formed, may become imperfect through the use of language, when it is unsuccessfully intended to agree with the idea of some other person and denominated by a current term. In the case of mixed modes and their names, therefore, the compatibility of their elements and the possible existence of their objects are not enough to secure their reality and their complete adequacy; in order to be adequate they must, further, exactly conform to the meaning connected with their names by their author, or in common use. Simple ideas are best off, according to Locke, in regard both to reality and to adequacy. For the most part, it is true, they are not accurate copies of the real qualities, of things, but only the regular effects of the powers of things. But although real qualities are thus only the causes and not the patterns of sensations, still simple ideas, by their constant correspondence with real qualities, sufficiently fulfill their divinely ordained end, to serve us as instruments of knowledge, i.e. in the discrimination of things.--An unreal and inadequate idea becomes false only when it is referred to an object, whether this be the existence of a thing, or its true essence, or an idea of other things. Truth and error belong always to affirmations or negations, that is, to (it may be, tacit) propositions. Ideas uncombined, unrelated, apart from judgments, ideas, that is, as mere phenomena in the mind, are neither true nor false.

Knowledge is defined as the "perception of the connexion and agreement, or disagreement and repugnancy" of two ideas; truth, as "the right joining or separating of signs, i.e. ideas or words." The object of knowledge is neither single ideas nor the relations of ideas to things, but the relations of ideas among themselves This view was at once paradoxical and pregnant. If all cognition, as Locke suggests in objection to his own theory, consists in perceiving the agreement or disagreement of our ideas, are not the visions of the enthusiast and the reasonings of sober thinkers alike certain? are not the propositions, A fairy is not a centaur, and a centaur is a living being, just as true as that a circle is not a triangle, and that the sum of the angles of a triangle is equal to two right angles? The mind directly perceives nothing but its own ideas, but it seeks a knowledge of things! If this is possible it can only be indirect knowledge--the mind knows things through its ideas, and possesses criteria which show that its ideas agree with things.

Two cases must be clearly distinguished, for a considerable number of our ideas, viz., all complex ideas except those of substances, make no claim to represent things, and consequently cannot represent them falsely. For mathematical and moral ideas and principles, and the truth thereof, it is entirely immaterial whether things and conditions correspondent to them exist in nature or not. They are valid, even if nowhere actualized; they are "eternal truths," not in the sense that they are known from childhood, but in the sense that, as soon as known, they are immediately assented to.[1] The case is different, however, with simple ideas and the ideas of substances, which have their originals without the mind and which are to correspond with these. In regard to the former we may always be certain that they agree with real things, for since the mind can neither voluntarily originate them (e.g. cannot produce sensations of color in the dark) nor avoid having them at will, but only receive them from without, they are not creatures of the fancy, but the natural and regular productions of external things affecting us. In regard to the latter, the ideas of substances, we may be certain at least when the simple ideas which compose them have been found so connected in experience. Perception has an external cause, whose influence the mind is not able to withstand. The mutual corroboration furnished by the reports of the different senses, the painfulness of certain sensations, the clear distinction between ideas from actual perception and those from memory, the possibility of producing and predicting new sensations of an entirely definite nature in ourselves and in others, by means of changes which we effect in the external world (e.g. by writing down a word)--these give further justification for the trust which we put in the senses. No one will be so skeptical as to doubt in earnest the existence of the things which he sees and touches, and to declare his whole life to be a deceptive dream. The certitude which perception affords concerning the existence of external objects is indeed not an absolute one, but it is sufficient for the needs of life and the government of our actions; it is "as certain as our happiness or misery, beyond which we have no concernment, either of knowing or being." In regard to the past the testimony of the senses is supplemented by memory, in which certainty [in regard to the continued existence of things previously perceived] is transformed into high probability; while in regard to the existence of other finite spirits, numberless kinds of which may be conjectured to exist, though their existence is quite beyond our powers of perception, certitude sinks into mere (though well-grounded) faith.

[Footnote 1: Thus it results that knowledge, although dependent on experience for all its materials, extends beyond experience. The understanding is completely bound in the reception of simple ideas; less so in the combination of these into complex ideas; absolutely free in the act of comparison, which it can omit at will; finally, again, completely bound in its recognition of the relation in which the ideas it has chosen to compare stand to one another. There is room for choice only in the intermediate stage of the cognitive process; at the beginning (in the reception of the simple ideas of perception, a, b, c, d), and at the end (in judging how the concepts a b c and a b d stand related to each other), the understanding is completely determined.]

More certain than our sensitive knowledge of the existence of external objects, are our immediate or intuitive knowledge of our own existence and our mediate or demonstrative knowledge of the existence of God. Every idea that we have, every pain, every thought assures us of our own existence. The existence of God, however, as the infinite cause of all reality, endowed with intelligence, will, and supreme power, is inferred from the existence and constitution of the world and of ourselves. Reality exists; the real world is composed of matter in motion and thinking beings, and is harmoniously ordered. Since it is impossible for any real being to be produced by nothing, and since we obtain no satisfactory answer to the question of origin until we rise to something existent from all eternity, we must assume as the cause of that which exists an Eternal Being, which possesses in a higher degree all the perfections which it has bestowed upon the creatures. As the cause of matter and motion, and as the source of all power, this Being must be omnipotent; as the cause of beauty and order in the world, and, above all, as the creator of thinking beings, it must be omniscient. But these perfections are those which we combine in the idea of God.

Intuitive knowledge is the highest of the three degrees of knowledge. It is gained when the mind perceives the agreement or disagreement of two ideas at first sight, without hesitation, and without the intervention of any third idea. This immediate knowledge is self-evident, irresistible, and exposed to no doubt. Knowledge is demonstrative when the mind perceives the agreement (or disagreement) of two ideas, not by placing them side by side and comparing them, but through the aid of other ideas. The intermediate links are called proofs; their discovery is the work of the reason, and quickness in finding them out is termed sagacity. The greater the number of the intermediate steps, the more the clearness and distinctness of the knowledge decreases, and the more the possibility of error increases. In order for an argument (e. g, that a = d) to be conclusive, every particular step in it (a = b, b = c, c = d) must possess intuitive certainty. Mathematics is not the only example of demonstrative knowledge, but the most perfect one, since in mathematics, by the aid of visible symbols, the full equality and the least differences among ideas may be exactly measured and sharply determined.

Besides real existence Locke, unsystematically enough, enumerates three other sorts of agreement between ideas,--in the perception of which he makes knowledge consist,--viz., identity or diversity (blue is not yellow), relation (when equals are added to equals the results are equal), and coexistence or necessary connexion (gold is fixed). We are best off in regard to the knowledge of the first of these, "identity or diversity," for here our intuition extends as far as our ideas, since we recognize every idea, as soon as it arises, as identical with itself and different from others. We are worst off in regard to "necessary connexion." We know something, indeed, concerning the incompatibility or coexistence of certain properties (e. g, that the same object cannot have two different sizes or colors at the same time; that figure cannot exist apart from extension): but it is only in regard to a few qualities and powers of bodies that we are able to discover dependence and necessary connexion by intuitive or demonstrative thought, while in most cases we are dependent on experience, which gives us information concerning particular cases only, and affords no guarantee that things are the same beyond the sphere of our observation and experiment. Since empirical inquiry furnishes no certain and universal knowledge, and since the assumption that like bodies will in the same circumstances have like effects is only a conjecture from analogy, natural science in the strict sense does not exist. Both mathematics and ethics, however, belong in the sphere of the demonstrative knowledge of relations. The principles of ethics are as capable of exact demonstration as those of arithmetic and geometry, although their underlying ideas are more complex, more involved, hence more exposed to misunderstanding, and lacking in visible symbols; though these defects can, and should, in part be made good by careful and strictly consistent definitions. Such moral principles as "where there is no property there is no injustice," or "no government allows absolute liberty," are as certain as any proposition in Euclid.

The advantage of the mathematical and moral sciences over the physical sciences consists in the fact that, in the former, the real and nominal essences of their objects coincide, while in the latter they do not; and, further, that the real essences of substances are beyond our knowledge. The true inner constitution of bodies, the root whence all their qualities, and the coexistence of these, necessarily proceed, is completely unknown to us; so that we are unable to deduce them from it. Mathematical and moral ideas, on the other hand, and their relations, are entirely accessible, for they are the products of our own voluntary operations. They are not copied from things, but are archetypal for reality and need no confirmation from experience. The connexion constituted by our understanding between the ideas crime and punishment (e. g, the proposition: crime deserves punishment) is valid, even though no crime had ever been committed, and none ever punished. Existence is not at all involved in universal propositions; "general knowledge lies only in our own thoughts, and consists barely in the contemplation of our own abstract ideas" and their relations. The truths of mathematics and ethics are both universal and certain, while in natural science single observations and experiments are certain, but not general, and general propositions are only more or less probable. Both the particular experiments and the general conclusions are of great value under certain circumstances, but they do not meet the requirements of comprehensive and certain knowledge.

The extent of our knowledge is very limited--much less, in fact, than that of our ignorance. For our knowledge reaches no further than our ideas, and the possibility of perceiving their agreements. Many things exist of which we have no ideas--chiefly because of the fewness of our senses and their lack of acuteness--and just as many of which our ideas are only imperfect. Moreover, we are often able neither to command the ideas which we really possess, or at least might attain, nor to perceive their connexions. The ideas which are lacking, those which are undiscoverable, those which are not combined, are the causes of the narrow limits of human knowledge.

There are two ways by which knowledge may be extended: by experience, on the one hand, and, on the other, by the elevation of our ideas to a state of clearness and distinctness, together with the discovery and systematic arrangement of those intermediate ideas which exhibit the relation of other ideas, in themselves not immediately comparable. The syllogism, as an artificial form, is of little value in the perception of the agreements between these intermediate and final terms, and of none whatever in the discovery of the former. Analytical and identical propositions which merely explicate the conception of the subject, but express nothing not already known, are, in spite of their indefeasible certitude, valueless for the extension of knowledge, and when taken for more than verbal explanations, mere absurdities. Even those most general propositions, those "principles" which are so much talked of in the schools, lack the utility which is so commonly ascribed to them. Maxims are, it is true, fit instruments for the communication of knowledge already acquired, and in learned disputations may perform indispensable service in silencing opponents, or in bringing the dispute to a conclusion; but they are of little or no use in the discovery of new truth. It is a mistake to believe that special cases (as 5 = 2 + 3, or 5 = 1 + 4) are dependent on the truth of the abstract rule (the whole is equal to the sum of its parts), that they are confirmed by it and must be derived from it. The particular and concrete is not only as clear and certain as the general maxim, but better known than this, as well as earlier and more easily perceived. Nay, further, in cases where ideas are confused and the meanings of words doubtful, the use of axioms is dangerous, since they may easily lend the appearance of proved truth to assertions which are really contradictory.

Between the clear daylight of certain knowledge and the dark night of absolute ignorance comes the twilight of probability. We find ourselves dependent on opinion And presumption, or judgment based upon probability, when experience and demonstration leave us in the lurch and we are, nevertheless, challenged to a decision by vital needs which brook no delay. The judge and the historian must convince themselves from the reports of witnesses concerning events which they have not themselves observed; and everyone is compelled by the interests of life, of duty, and of eternal salvation to form conclusions concerning things which lie beyond the limits of his own perception and reflective thought, nay, which transcend all human experience and rigorous demonstration whatever. To delay decision and action until absolute certainty had been attained, would scarcely allow us to lift a single finger. In cases concerning events in the past, the future, or at a distance, we rely on the testimony of others (testing their reports by considering their credibility as witnesses and the conformity of the evidence to general experience in like cases); in regard to questions concerning that which is absolutely beyond experience, e.g. higher orders of spirits, or the ultimate causes of natural phenomena, analogy is the only help we have. If the witnesses conflict among themselves, or with the usual course of nature, the grounds pro And con must be carefully balanced; frequently, however, the degree of probability attained is so great that our assent is almost equivalent to complete certainty. No one doubts,--although it is impossible for him to "know,"--that Caesar conquered Pompey, that gold is ductile in Australia as elsewhere, that iron will sink to-morrow as well as to-day. Thus opinion supplements the lack of certain knowledge, and serves as a guide for belief and action, wherever the general lot of mankind or individual circumstances prevent absolute certitude.

Although in this twilight region of opinion demonstrative proofs are replaced merely by an "occasion" for "taking" a given fact or idea "as true rather than false," yet assent is by no means an act of choice, as the Cartesians had erroneously maintained, for in knowledge it is determined by clearly discerned reasons, and in the sphere of opinion, by the balance of probability. The understanding is free only in combining ideas, not in its judgment concerning the agreement or the repugnancy of the ideas compared; it lies within its own power to decide whether it will judge at all, and what ideas it will compare, but it has no control over the result of the comparison; it is impossible for it to refuse its assent to a demonstrated truth or a preponderant probability.

In this recognition of objective and universally valid relations existing among ideas, which the thinking subject, through comparisons voluntarily instituted, discovers valid or finds given, but which it can neither alter nor demur to, Locke abandons empirical ground (cf. p. 155) and approaches the idealists of the Platonizing type. His inquiry divides into two very dissimilar parts (a psychological description of the origin of ideas and a logical determination of the possibility and the extent of knowledge), the latter of which is, in Locke's opinion, compatible with the former, but which could never have been developed from it. The rationalistic edifice contradicts the sensationalistic foundation. Locke had hoped to show the value and the limits of knowledge by an inquiry into the origin of ideas, but his estimate of this value and these limits cannot be proved from the a posteriori origin of ideas--it can only be maintained in despite of this, and stands in need of support from some (rationalistic) principle elsewhere obtained. Thinkers who trace back all simple ideas to outer and inner perception we expect to reject every attempt to extend knowledge beyond the sphere of experience, to declare the combinations of ideas which have their origin in sensation trustworthy, and those which are formed without regard to perception, illusory; or else, with Protagoras, to limit knowledge to the individual perceiving subject, with a consequent complete denial of its general validity. But exactly the opposite of all these is found in Locke. The remarkable spectacle is presented of a philosopher who admits no other sources of ideas than perception and the voluntary combination of perceptions, transcending the limits of experience with proofs of the divine existence, viewing with suspicion the ideas of substance formed at the instance of experience, and reducing natural science to the sphere of mere opinion; while, on the other hand, he ascribes reality and eternal validity to the combinations of ideas formed independently of perception, which are employed by mathematics and ethics, and completely abandons the individualistic position in his naïve faith in the impregnable validity of the relations of ideas, which is evident to all who turn their attention to them. The ground for the universal validity of the relations among ideas as well as of our knowledge of them, naturally lies not in their empirical origin (for my experience gives information to me alone, and that only concerning the particular case in question), but in the uniformity of man's rational constitution. If two men really have the same ideas--not merely think they have because they use similar language--it is impossible, according to Locke, that they should hold different opinions concerning the relation of their ideas. With this conviction, that the universal validity of knowledge is rooted in the uniformity of man's rational constitution, and the further one, that we attain certain knowledge only when things conform to our ideas, Locke closely approaches Kant; while his assumption of a fixed order of relations among ideas, which the individual understanding cannot refuse to recognize, and the typical character assigned to mathematics, associate him with Malebranche and Spinoza. In view of these points of contact with the rationalistic school and his manifold dependence on its founder, we may venture the paradox, that Locke may not only be termed a Baconian with Cartesian leanings, but (almost) a Cartesian influenced by Bacon. The possibility must not be forgotten, however, that rationalistic suggestions came to him also from Galileo, Hobbes, and Newton.[1]

[Footnote 1: Cf. the article by Benno Erdmann cited p. 156, note.]

Intermediate between knowledge and opinion stands faith as a form of assent which is based on testimony rather than on deductions of the reason, but whose certitude is not inferior to that of knowledge, since it is a communication from God, who can neither deceive nor be deceived. Faith and the certainty thereof depend on reason, in so far as reason alone can determine whether a divine revelation has really been made and the meaning of the words in which the revelation has come down to us. In determining the boundaries of faith and reason Locke makes use of the distinction--which has become famous--between things above reason, according to reason, and contrary to reason. Our conviction that God exists is according to reason; the belief that there are more gods than one, or that a body can be in two different places at the same time, contrary to reason; the former is a truth which can be demonstrated on rational grounds, the latter an assumption incompatible with our clear and distinct ideas. In the one case revelation confirms a proposition of which we were already certain; in the other an alleged revelation is incapable of depriving our certain knowledge of its force. Above reason are those principles whose probability and truth cannot be shown by the natural use of our faculties, as that the dead shall rise again and the account of the fall of part of the angels. Among the things which are not contrary to reason belong miracles, for they contradict opinion based on the usual course of nature, it is true, but not our certain knowledge; in spite of their supernatural character they deserve willing acceptance, and receive it, when they are well attested, whereas principles contrary to reason must be unconditionally rejected as a revelation from God. Locke's demand for the subjection of faith to rational criticism assures him an honorable place in the history of English deism. He enriched the philosophy of religion by two treatises of his own: The Reasonableness of Christianity 1695, and three Letters on Tolerance 1689-1692. The former transfers the center of gravity of the Christian religion from history to the doctrine of redemption; the Letters Demand religious freedom, mutual tolerance among the different sects, and the separation of Church and State. Those sects alone are to receive no tolerance which themselves exercise none, and which endanger the well-being of society; together with atheists, who are incapable of taking oaths. In other respects it is the duty of the state to protect all confessions and to favor none.

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