Folk and traditional music doesn't exist on its own. Its part of the common culture of a community. The thing is, it often has value outside of that community, and can be adopted and adapted by other communities.

All people are "folk", and all of them belong to communities of one sort or another. In recent years, a lot of long standing communities have disappeared. Others have lost parts of their common culture, such as the music. Other communities still, such as song circles, folk clubs, church groups, schools, and academics, have adopted and adapted musical artifacts from these more traditional communities.

It would be a mistake to say that the adopter/adapter communities had in become part of the traditions that they drew material from, since the songs and music, of necessity, have different meanings and functions in the new community.

However, the music and songs have become a part of the common culture of the adopter/adapter group, who are then the "folk" of their own community.

The common culture of this new community may include music derived from, and inspired by the music that has been adopted/adapted, and, in this way, even "singer/songwriter" music is folk music.