Music Theory Basics: Notes, Scales, Intervals and Chords Explained

Music theory has a reputation for being dry, full of rules and Latin-sounding words. In reality, the core ideas are small and surprisingly logical. Western music is built from just twelve notes, a handful of distances between them, and a few repeating patterns.

Keep a keyboard nearby while you read. A real one is great, but the online piano works just as well, because the keyboard is the clearest picture of music theory ever invented.

The twelve notes and the octave

Look at a piano keyboard and you will see a pattern of white keys with black keys in groups of two and three. That pattern repeats all the way along. Each repeat contains exactly twelve different notes: seven white keys and five black keys.

The white keys are named with the letters A to G. The white key just to the left of any group of two black keys is C, and it is the usual starting point. From there the white keys go C, D, E, F, G, A, B, and then the next C begins the pattern again.

The distance from one C to the next C is called an octave. The two notes sound like higher and lower versions of the same thing, which is why they share a name.

Sharps, flats, half steps and whole steps

The black keys are named after their white neighbours. A sharp ( ) raises a note by the smallest step, and a flat (b) lowers it. So the black key between C and D can be called C or Db. Both names describe the same key.

That smallest step, from any key to the very next key with nothing in between, is a half step (also called a semitone). Two half steps make a whole step (a tone). C to C is a half step; C to D is a whole step, because the black key sits between them.

Notice one important detail: there is no black key between E and F, or between B and C. Those pairs of white keys are only a half step apart. This small quirk is the reason scales have their particular shape.

The major scale formula

A scale is a set of notes played in order from one note up to its octave. The most important one to learn first is the major scale, the bright, familiar sound of "do re mi fa so la ti do".

Every major scale follows the same pattern of steps:

Whole, Whole, Half, Whole, Whole, Whole, Half (W-W-H-W-W-W-H)

Start on C and follow the formula: C to D (whole), D to E (whole), E to F (half), F to G (whole), G to A (whole), A to B (whole), B to C (half). You land on every white key and no black keys. That is why C major is the first scale most pianists learn.

Try it yourself

The same formula works from any of the twelve notes: one rule, twelve scales.

Find any G on the keyboard.
Count out the formula W-W-H-W-W-W-H, moving one key for a half step and two keys for a whole step.
You should play G, A, B, C, D, E, F , G. One black key appears, F , because the formula demands it.
Now try starting on F. This time you will need one flat, Bb.

Minor scales and their darker colour

The natural minor scale uses a different pattern: W-H-W-W-H-W-W. Start on A and follow it, and once again you play only white keys: A, B, C, D, E, F, G, A. Yet it sounds noticeably darker or more serious than C major.

C major and A minor share exactly the same notes. They are called relative keys. The difference is which note feels like "home". Every major key has a relative minor that starts on its sixth note.

Intervals: measuring the distance between notes

An interval is the distance between two notes. Musicians name intervals by counting letter names and then describing their exact size in half steps. Here are the ones to know first, measured upwards from C:

Intervals matter because they give music its emotional colour. A major third sounds open and happy; a minor third sounds softer and sadder. The perfect fifth sounds stable and strong.

Major second: C to D, 2 half steps
Minor third: C to Eb, 3 half steps
Major third: C to E, 4 half steps
Perfect fourth: C to F, 5 half steps
Perfect fifth: C to G, 7 half steps
Octave: C to the next C, 12 half steps

Building triads, the simplest chords

A chord is three or more notes played together. The basic chord is the triad, built by stacking two thirds on top of each other. Choose a starting note, called the root, then skip a note, take the next, skip again, take the next.

Play C-E-G and then C-Eb-G. Only one note moves by a single half step, yet the mood changes completely.

Major triad: root, major third, perfect fifth. C, E and G (4 half steps, then 3).
Minor triad: root, minor third, perfect fifth. A, C and E (3 half steps, then 4).
Diminished triad: two minor thirds. B, D and F (3, then 3).

Keys: putting scales and chords together

When a song is "in C major", it mostly uses the notes of the C major scale, and C feels like home. If you build a triad on each note of that scale, using only notes from the scale, you get the seven chords of the key: C, Dm, Em, F, G, Am and B diminished. Many songs use just a few of these, especially the chords built on the first, fourth and fifth notes (C, F and G in this key).

Each major key has its own number of sharps or flats, called its key signature. G major has one sharp, D major has two, F major has one flat. The interactive circle of fifths lays all twelve keys out in order, with their key signatures, relative minors and the chords in each key, so you can see how they connect.

Where to go from here

Theory sticks best when you hear it. A routine for the next week:

Twelve notes, two kinds of step, one scale formula and a way to stack thirds: that is the foundation nearly everything else in theory is built on. Learn these with your ears and fingers as well as your eyes, and the rest will feel like natural next steps rather than new rules.

Play the C major and A minor scales slowly every day and listen to the difference in mood.
Work out one new major scale a day using W-W-H-W-W-W-H.
Play the major and minor triad on every white key and say each chord's name aloud.
Check your answers with the scale and chord finder, which shows and plays the notes of common scales and chords in all twelve keys.