Key

A chord is "in-key" if its chord tones are composed of notes that exist in the key you're playing in.

To derive the chords in the C major scale, we follow this process:

• for each scale degree, build off the 1-3-5.
• if the 1-3-5 notes all exist in the C major scale, then the chord is good
• if the note does not exist in the C major scale, then it needs to be flattened
  • ex. building 1-3-5 off the second scale degree of C major is D-G♭-A. Since G♭ is not in the key of C major, it needs to be flattened to F. Therefore, the second chord of C major is D minor.

Think of the notes of a key as different pieces of punctuation. The root is like the period, since it brings some sense of finality. The 4th is like a comma, which implies there is more to come.

The 3rd is the most melodic part of the key. To make phrases sound more melodic, give more prominence to the 3rd.

Relative key

Two keys are relative if they contain all of the same notes

• ex. C and Am

The relative minor is 3 semitones below the tonic of the major scale

• ex. 3 semitones below the C is A, meaning that the relative minor of C is Am

Modulation

• Also known as key change

Modulation to the subdominant key often creates a sense of musical relaxation, as opposed to modulation to the dominant (fifth note of the scale), which increases tension.

• ex. If we are playing in C major, modulation to the subdominant means a key change to F