A commonly-used convention for describing scale structure is a number system that uses the major scale as the point of reference. The system works as follows:
- The number “1” always represents the key that you are in.
- Numbers are assigned to each note in the major scale in ascending order.
- In the key of C: C=1, D=2, E=3, F=4, G=5, A=6, B=7
Thus, the major scale is said to have a scale structure of 1-2-3-4-5-6-7.
Special Note: There is nothing sacred about the major scale. The choice of the major scale as the point of reference is arbitrary, used as a convenient point of reference for the simple reason that it is so widely used compared to other scale types in Western music.
Of course, any combination of notes is theoretically possible when building scales. Any of the scales degrees (number) can be modified by a sharp or flat, as shown in the commonly-used examples below…
Mixolydian Scale (structure = 1-2-3-4-5-6-b7), key of C
Harmonic Minor Scale (structure = 1-2-b3-4-5-b6-7), key of C
Lydian Scale (structure = 1-2-3-#4-5-6-7), key of C
Don’t worry about the details right now. For the moment, it is sufficient to understand the concept of scale structure, scale degrees, and the number system. There will be plenty of time to study-practice as you continue your studies of scales, key signatures, chords, chord changes, and ear-training.