You Are Reading the First 6 FREE Chapters (470 pages)
4.2.2Major Scale Intervals and the Tonic Note
Figure 15 (below) clarifies the logic of interval names a bit:
FIGURE 15: C Major Scale with Intervals Named
For reasons that will become clearer as you get better acquainted with intervals and scales and chords, all of the intervals are named with reference to the first note (the tonic note) of the major scale. For example, major second refers to the second note of the major scale, if you start from the tonic note.
The major scale has only eight notes. That’s why none of the intervals has a name higher than “seventh,” even though there are 12 different intervals.
(The intervals are not named after the notes of the chromatic scale because the chromatic scale by itself has no use as a “musical” scale.)