Every major-scale consists of two “equal” parts called Tetrachords. Each of these parts consists of two whole-tone-steps (WT) and one half-tone-step (HT) i.e.
WT WT HT WT WT HT
example
C (WT) D (WT) E (HT) F G (WT) A (WT) B (HT) C
Note in the example above HT is where there is no black not between the white notes i.e. between E and F and the B and C notes.
