Folk music, in the original sense of the term, is music by and of the people. Folk music arose, and best survives, in societies not yet affected by mass communication and the commercialisation of culture. It normally was shared and performed by the entire community (not by a special class of expert performers), and was transmitted by word of mouth.
During the 20th century, the term folk music took on a second meaning: it describes a particular kind of popular music which is culturally descended from or otherwise influenced by traditional folk music. Like other popular music, this kind of folk music is most often performed by experts and is transmitted in organised performances and commercially distributed recordings.
Defining folk music
Because of the changing meaning of "folk music", people asked to define it give widely varying answers. When Gene Shay, co-founder and host of the Philadelphia Folk Festival, was asked to define folk music in an April 2003 interview, he gave an answer similar to the definition above: "In the strictest sense, it's music that is rarely written for profit. It's music that has endured and been passed down by oral tradition. [...] And folk music is participatory—you don't have to be a great musician to be a folk singer. [...] And finally, it brings a sense of community. It's the people's music." The jazz performer Louis Armstrong, is famously credited with saying, "All music is folk music, leastwise I ain't never heard a horse sing". This emphasises the universality of people's love for music (which folk music also attests), and aptly expresses Armstrong's warm personal connection to his audience, but it also misses a distinction. Armstrong was not a folk musician, but a gifted performer within a sophisticated popular music tradition, which by his time had evolved to be very different from its folk origins.
The English term folk, which gained usage in the 18th century to refer to peasants or non-literate peoples, is related to the German word Volk (meaning people or nation). 'Folk music' in the strict, original sense of the term covers only that music which arises from the speech and circumstances of the common people of a culture. It matters not whether that culture is 18th century rural Suffolk or 21st century inner-city Manchester; the material which can truly be identified as folk music (and especially folk song, because language is more important than musicality in expressing the condition of life) must be that music and song which is created by the common people in the process of expressing themselves.
Music which was created in this way before the rise of mass communications and mass media is now termed "traditional music," i.e., the traditional music of particular ethnic groups learned by ear, that is, as part of an oral tradition, and played on acoustic instruments or sung with unaccompanied voice. In those days (bygone, in most of the Western world, as we shall see), the motivating forces behind the creation of folk music were those of communication, teaching and entertainment. These needs of the community were met from within the community, through the medium of folk song in particular.
Variation in folk music
Music transmitted by word of mouth though a community will, in time, develop many variants, because this kind of transmission cannot produce word-for-word and note-for-note accuracy. Indeed, many traditional folk singers are quite creative and deliberately modify the material they learn.
Because variants proliferate naturally, it is naïve to believe that there is such a thing as the "authentic" version of a ballad such as "Barbara Allen." Field researchers in folk song (see below) have encountered countless versions of this ballad throughout the English-speaking world, and these versions often differ greatly from each other. None can reliably claim to be the original, and it is quite possible that whatever the "original" was, it ceased to be sung centuries ago. Any version can lay an equal claim to authenticity, so long as it is truly from a traditional folk-singing community and not the work of an outside editor.
Cecil Sharp had an influential idea about the process of folk variation: he felt that the competing variants of a folk song would undergo a process akin to biological natural selection: only those new variants that were the most appealing to ordinary singers would be picked up by others and transmitted onward in time. Thus, over time we would expect each folksong to become aesthetically ever more appealing--it would be collectively composed to perfection, as it were, by the community.
Many feel, examining the folksongs that Sharp collected from traditional singers, that there is something to this theory. The Sharp material often shows a very striking, simple beauty, and is there is little tawdry, cheap material that it might have temporarily picked up from external sources. This suggests that such material did indeed get "filtered out" by the collective efforts of the community. On the other hand, there is also evidence to support the view that transmission of folk songs can be rather sloppy. Occasionally, collected folk song versions include material or verses incorporated from different songs that makes little sense in its context. A perfect process of natural selection would not have permitted these incoherent versions to survive.