There are two seemingly self-evident truths concerning the harmonic practices of popular music. The first, which finds clear expression in Adorno, is that such music's harmonic language is both detrimentally limited and static. The harmonic repertoire is considered to consist of a few formulae (Adorno deals with them in terms of standardisation: see Middleton 1990, p. 45ff.), by means of which song-writers string together their songs, uninfluenced by the song's content. For the expert listener, therefore, popular music should be uninteresting: it is only its psycho-economic dimension which makes it worthy of study. This tends also to be the conclusion of established musicology, except that there it is felt such ‘extra-musical’ speculation is best left to the sociologist. The second truth is that the differences between Afro-American-derived styles are material, since our identities are so strongly incorporated in the styles we use: We mark out the differences between genres and styles partly by reference to contrasts in the way this stock of techniques and sounds is used. (Middleton 1990, p. 88) Since harmony is not only at the forefront of traditional analytical investigation, but also forms an important initial focus for songwriters, it may well be assumed that it is therefore an important factor in enabling us to distinguish, for example, ‘rock’ from ‘pop’ from ‘soul’. However, the material reality behind these differences of style has rarely been subject to systematic investigation.