What even are musical keys?

Keys are just organised sets of notes

A key is simply a collection (scale) of seven notes arranged so that the first note feels like “home”; its chords are just stacked notes from that scale.

• The home note is called the tonic.

• All the other notes in the key can feel stable/unstable, tense, or resolved in relation to the tonic.

That’s all there is to a key: a scale of seven notes and the chords built with them.

Major vs minor is about how “home” is built

Major and minor are not opposites, they’re just constructed differently. The notes in the home chord for major and minor keys follow distinct but predictable patterns because of their scales.

In major scales, the 3rd note is 4 semitones (half-steps) up from home; in minor scales it’s just 3 semitones up. The distance between notes is called an interval, and the interval between the tonic and the 3rd note of the diatonic scale is called a “third”. Wacky naming, eh? This one small change creates a palpable shift in mood:

• Major keys tend to feel stable and positive because the tonic (or “home”) chord is built on note intervals that resonate well with one another, sounding full and bright and natural.

• Minor keys tend to feel darker because the tonic (home) chord contains intervals where notes are closer together, creating more tension and less brightness than the equivalent “home” sound in a major key.