Starting in the mid-20th century a new form of popular folk music evolved from traditional folk music. This process and period is called the (second) folk revival and reached a zenith in the 1960s.
From a historical perspective, traditional folk music had these characteristics
It was transmitted through an oral tradition. Before the twentieth century, ordinary farm workers and factory workers were usually illiterate. They acquired songs by memorizing them. Primarily, this was not mediated by books, recorded or transmitted media. Singers may extend their repertoire using broadsheets, song books or CDs, but these secondary enhancements are of the same character as the primary songs experienced in the flesh.
The music was often related to national culture. It was culturally particular - from a particular region or culture. In the context of an immigrant group, folk music acquires an extra dimension for social cohesion. It is particularly conspicuous in the United States, where Polish Americans, Scottish Americans, Irish Americans, Asian Americans and others strive to emphasis differences from the mainstream. They will learn songs and dances that originate in the countries where their grandparents came from.
They commemorate historical and personal events. On certain days of the year, such as Easter, May Day and Christmas, particular songs celebrate the yearly cycle. Weddings, birthdays and funerals may also be noted with songs, dances and special costumes. Religious festivals often have a folk music component. Choral music at these events brings children and non-professional singers to participate in a public arena, giving an emotional bonding that is unrelated to the aesthetic qualities of the music.
The songs have been performed, by custom, over a long period of time, usually several generations.
As a side-effect, the following characteristics are sometimes present:
There is no copyright on the songs. There are hundreds of folk songs from the nineteenth century which have known authors. However, they have continued in oral tradition, to the point where they are classified as "Traditional", for purposes of music publishing. This has become much less frequent since the 1970s. Today, almost every folk song that is recorded is credited with an arrangement.
Fusion of cultures. In the same way that people can have a mixed background, with parents originating in different continents, so too music can be a blend of influences. A particular rhythmic pattern, or a characteristic instrument, is enough to give a traditional feel to music, even when it has been composed recently. It is easy to recognize the presence of a bagpipe or a tabla in a piece of music. The young are usually much less offended by the dilution or adaptation of songs this way. Equally an electric guitar can be added to an old song. The relevant factors may include instrumentation, tunings, voicings, phrasing, subject matter, and even production methods.