Text: An interval in music is distance (between the notes) expressed in terms of difference in pitch. Sound the two tones to the right. The ear immediately detects that one tone is higher than the other. The eye detects the interval which is represented graphically by two signs (notes), one of which is higher on the staff than the other. This audible and visible highness is, in music, distance or interval. This distance can be measured. To measure an interval we must have a definite and unchangeable unit of measure. In expressing intervals by name several technical terms are employed. For example: this interval is a Major Sixth because there are six steps (inclusive) between the two tones. We infer from the word Major that there are other kinds of sixths, and from the word sixth we infer that in naming intervals, something is counted, something which in this example contains six distinct units.

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