Scales and keys

Choosing seven notes.

Major and minor

The major scale follows a pattern of tone and semitone steps; the minor scale flattens the third, sixth and seventh in its natural form and has variants.

Twelve semitones divide the octave in equal temperament.
The key signature tells you which notes the piece draws on.

Modes and other scales

Dorian, Mixolydian and the rest are rotations of the same set of notes with a different home. Pentatonic and blues scales are used worldwide.