DIATONIC

in music, originally, one of the three tetrachords basic to ancient Greek theory; more generally, any stepwise arrangement of the seven natural pitches forming an octave devoid of chromatic alterations, in particular the major and minor scales that evolved from the medieval and Renaissance church modes in conjunction with the rise of diatonic harmony. The increasing irrelevance of the old modal system caused the 16th-century Humanist Glareanus to propose two additional modes, Aeolian and Ionian, based on A and C, respectively, and identical in every way with the modern major and natural minor. The major scale consists of two identical disjunct tetrachords, each comprising two wholetone steps topped by a semitone, while the minor scale in its natural form consists of one tetrachord with the semitone in the middle and another with the semitone at the bottom. Given the crucial importance of the so-called leading tone (the semitone between the seventh and eighth scalar steps) for diatonic harmony, however, natural minor in practice tends to yield to the need for chromatic alteration of the seventh step. The harmonic minor that results is, strictly speaking, no longer a diatonic scale, unlike melodic minor, which simply borrows its upper tetrachord from the parallel major, i.e., the major scale beginning and ending on the same pitch. Due to the close, indeed causal connections between diatonic harmony and the major and minor scales, diatonic scale degrees are often built on the corresponding pitches. Thus, the first step is often referred to as the tonic, the second as the supertonic, third as the mediant, fourth as the subdominant, fifth as the dominant, sixth as the submediant, and seventh as the leading tone. However, heptatonic (seven-note) diatonic scales occur also well beyond the confines of Western art music, including European and American folk monophony, as well as African and Asian music, and therefore, the theoretical value of such linguistic usage is questionable. It should be noted that the rapidly developing instrumental music of 18th- and 19th-century Europe, with its increasing emphasis on expressiveness, favoured chromatic intrusions to the extent that, by the time of Wagner, diatonicism became relegated primarily to the popular and semipopular realms of musical creativity.