To identify the size and quality of an interval using a major scale for reference,
assume the bottom note of the interval is the tonic of a major scale.
1. If the upper note of the interval belongs to that major scale, then unisons,
4ths, 5ths and 8ves will be perfect, and 2nds, 3rds, 6ths, and 7ths will be
major.
2. If the upper note of the interval does not belong to that major scale, determine
by how many half steps it differs from that scale degree of the major scale.
Based on the half step differential, determine the quality.
