TONES IN SUCCESSIVE COMBINATION: MELODY
MUSIC DOES NOT CONSIST of any haphazard succession of tones, but of tones that form intervals, and which in turn give rise to larger tonal units that culminate in a melody. The smallest musical unit is thus the musical interval, and the first problem in the study of the psychological structure of melody is an examination of the nature of intervals which can be called musical.
The most obvious definition of an interval would be that it consists of two tones of different pitch. But that is not always so. Two successively presented tones may differ in pitch without forming an interval. For instance, if we begin with any tone and make a gradual transition in pitch up or down, as sliding a finger over a violin string, we do not hear a series of intervals, but a wail. Again, if we raise or lower the pitch of any tone slightly we do not hear an interval but the same tone somewhat modified, namely as sharp or flat. If a singer or player should sing or play off pitch to the extent of forming an interval with the true tone the effect would not be painful but ludicrous. Experimental results show that any one of two tones of an interval can be changed in pitch up to a certain point without changing the interval. All these facts indicate that an interval is more than merely a pitch difference between two tones, although without pitch differences there could be no intervals.
What then is an interval? It is a pitch difference between two tones of sufficient size or distance to produce the effect of two different tones, and not only of a slight pitch modification of the same tone. An interval consists of two definite pitch-