The reason why we find well-known folk-songs adapted to different airs is somewhat obvious, and the following explanation may be I think accepted. Where a singer reads a folk-song from a ballad sheet and does not know its particular tune, it is easy to believe that he uses one with which he is already familiar, or adapts one, or even composes an air from the stock musical phrases that he knows in other melodies. Thus we find folk-songs sung to many different airs, and this is not evolution. It may be noticed that in the lesser marked tunes, or rather less original airs, stock musical phrases are in use just as the stock phrases of the ballad-maker are employed by him over and over again. The folk-song singer looks for and welcomes these passages. They are conventional and are the most acceptable. Just as a child gives a better welcome to a story beginning “Once upon a time” than to a less hackneyed manner of opening, and as the folk-singer demands that every girl shall be “a fair damsel,” that the incident of the song shall happen “As I was a-walking one morning in May,” and that his mode of address shall be “I stepped up boldly to her,” or the like, so there are certain inevitable musical phrases in folk-music that one meets with in a particular type of melody. Waggish musicians are sometimes guilty of inventing “a folk-melody” for the purpose of deceiving and laughing at collectors. The collector, recognising the phrases he knows so well, may accept the tune as genuine. He is not wrong or ignorant in this; the musician has got possession of the material and spirit of folk-music, and then deception is easy. A man may have a Johnsonian method of diction without having the wit or learning of the great lexicographer, and might even pass off a short speech as a genuine one of the Doctor’s. These stock phrases are of course freely used in folk-music, and it is quite easy for a singer of folk-song legitimately to make an air for a ballad whose proper tune he may not know. This is another way in which variation of tunes occurs, and such results are frequently very puzzling to the expert. The singer may have remembered a passage of a melody and to this he has fitted other phrases that he is also familiar with. He is probably not conscious of the composite tune he is making,—he may even think that he is singing the correct tune. VI. THE QUALITY OF FOLK-SONG, AND ITS DIFFUSION The strongest and most valuable feature of folk-song is its earnestness and good faith. Though the quality of earnestness is indefinable it is the soul of art work, and its presence is ever felt.