Mode and key are concepts that are often confused. Let us see if we can clarify them.

We have just seen how the two modes, the major with its tonic or home pitch on C and the minor on A, are derived from the diatonic scale. However, if you use all twelve notes of the chromatic scale, you can construct both the major and the minor modes starting from any note at all. Whichever note you choose as tonic, starting from there you can pick out the correct sequence of half steps and whole steps. This is because the chromatic scale includes all possible half steps and whole steps.

Thanks to the chromatic scale, then, major and minor modes can be constructed starting on any pitch. These different positions for the modes are called keys. If the major mode is positioned on C, the music is said to be in the key of C major, or just “in C”; positioned on D, the key is D major. Likewise we have the keys of C minor, D minor, and — as there are twelve pitches in the chromatic scale — a grand total of twenty-four different keys (twelve major and twelve minor).