63.1Start with something completely familiar

C major triad:

C E G

D minor triad:

D F A

Combine their notes:

C D E F G A.

That gives six notes.

Only B is absent from the full C-major scale.

Already this sounds different from thinking:

C D E F G A B.

Why?

Because your mind sees:

C major + D minor

instead of:

seven consecutive scale steps.