Music theory basics: scales and chords

Labels, not rules

Music theory sounds like a pile of rules to memorise, but it is closer to a set of names for sounds you already hear. Once there are names for the difference between a bright song and a sad one, or for why a song feels finished, reading music, memorising pieces and talking with other musicians all get much easier. You can play without theory, but knowing it means you get more out of the same practice. At first, getting three ideas solid — semitones and whole tones, scales, and chords — is plenty.

Semitones and whole tones

Western music divides the octave into twelve semitones. On a piano, the distance between two directly adjacent keys is a semitone, and stepping up one key at a time, black keys included, brings you back to the same note name an octave higher after twelve steps. Two semitones make a whole tone. Looking at the white keys only, C to D has a black key between them and is a whole tone, but E to F and B to C have no black key and are semitones. Those two semitones are the key to a scale's character.

How the major scale is built

Starting on C and playing only the white keys — do, re, mi, fa, sol, la, ti, do — gives the most familiar major scale. Writing down the distances between the notes gives whole, whole, half, whole, whole, whole, half. The bright sound of the major scale comes from exactly this pattern of steps. So whichever note you start on, keeping the pattern produces a major scale with the same feel, bringing in black keys where needed. The starting note becomes the tonal centre of the piece, which is called its key.

• From the starting note, go up two whole tones
• Go up one semitone
• Go up three whole tones
• One more semitone brings you to the starting note an octave up

The minor scale and mood

Play the same white keys from A to A and you get the darker, calmer natural minor scale. Its steps are whole, half, whole, whole, half, whole, whole. Compared with the major scale, the biggest difference is that the third note from the start is a semitone lower, and that third does most of the work of separating bright from dark. Two keys that share the same notes, like C major and A minor, are called relative keys, and songs often move between them to shift the mood.

Chords are stacked notes

A chord is several notes sounded together. The most basic, the triad, is built by stacking three notes from a scale, skipping one each time. Starting on C gives C, E and G; the bottom note is called the root, the middle the third and the top the fifth. In the same way, starting on D gives D, F and A, and starting on G gives G, B and D. You can build one triad on each of the scale's seven notes, and those seven chords are the basic material used naturally in that key.

Major and minor chords

A triad's character is set by the distance from the root to the third. A third four semitones above the root gives a bright major chord; three semitones gives a darker minor chord. In both, the fifth sits seven semitones above the root. C, E, G is a major chord, and lowering the E a semitone makes it minor. In a major key, the chords on degrees I, IV and V are major, II, III and VI are minor, and VII is diminished, with a fifth narrowed by a semitone.

• Major: four semitones root to third, three from third to fifth
• Minor: three semitones root to third, four from third to fifth
• Diminished: two stacks of three semitones, so the fifth is a semitone narrower

The flow of a chord progression

Chords mean more in sequence than on their own. The I chord feels stable, like home; the V chord creates tension that wants to return to I; the IV chord steps away from home in between. That is why the progression I–IV–V–I has such a clear sense of ending and has been used in countless songs for a long time. Mixing in the minor VI and II chords adds colour within the same key. Listening to the accompaniment of songs you like and sensing whether the music is at home or away is a good way to start learning progressions.

How to learn theory

Theory read only from a book is quickly forgotten. Checking it by actually making the sounds, on a keyboard app or a real instrument, is what makes it stick in your ears and hands.

• Count semitones and whole tones while looking at a keyboard
• Build major scales from different notes using only the step pattern
• Alternate major and minor chords on the same root
• Find the chords of a song you like and mark the I, IV and V