What’s in a chord?

Notes

As already noted, in Western music there are twelve notes. After the twelfth, the pattern repeats - the next note sounds like the first one again, just higher. That repetition is called an octave.

Here’s the note C and two of its octaves:

All twelve notes are evenly spaced - the distance from one note to the next is always the same. Seven of them have letter names (A, B, C, D, E, F, G) and the other five are named with sharps (♯) or flats (♭). A sharp means “one note higher” and a flat means “one note lower,” so the note between C and D can be called C♯ (one up from C) or D♭ (one down from D) - same note, two names. The naming is just a historical convention - there’s nothing more “real” about a C than a C♯, and nothing more special or intimidating about a C♯ than a C.

Here are all twelve notes, in order:

On a guitar, each fret is one note higher than the last. Twelve frets up from any note brings you back to the same letter name, one octave higher.

Semitones and tones

A semitone is the smallest step you can take between two notes. On a guitar, it’s one fret. C to C♯ is a semitone. E to F is also a semitone, because there’s no sharp or flat between them.

A tone (or whole step) is two semitones - two frets. C to D is a tone.

That’s it. Every distance in music is built from these two units. When people talk about something being “a major third” or “a perfect fifth,” they’re really just describing a specific number of semitones.

Intervals

An interval is the distance between two notes, given a name. Instead of saying “seven semitones,” musicians say “a perfect fifth.” The names sound old-fashioned, but they’re just labels for specific semitone counts.

Here are the intervals within one octave. Listen to a few - notice how some sound stable and resolved while others feel tense or unsettled.

You don’t need to memorise all of these right now. The important ones for what comes next are the minor 3rd (3 semitones), the major 3rd (4 semitones), and the perfect 5th (7 semitones). These three intervals are the building blocks of chords.

Scales

A scale is a selection of notes from the twelve available, arranged in order from lowest to highest. Which notes you pick is determined by a pattern of intervals - a formula.

The most important scale in Western music is the major scale. Its formula is:

Here’s what that sounds like starting on C:

Start on any note and apply that formula, and you get a major scale. Start on C: C, D, E, F, G, A, B - that’s C major. Start on G: G, A, B, C, D, E, F♯ - that’s G major. The formula’s always the same; only the starting note changes.

C major is the only major scale with no sharps or flats - just the white keys on a piano. That’s why it’s usually taught first and used in examples: it’s the simplest case. But the formula works identically from any starting note; some keys just end up with more sharps or flats than others.

Try it yourself - pick any starting note:

Every major scale produces seven distinct notes. Those seven notes are the raw material for everything else in the key - the chords, the progressions, the solos. Choose a starting note, apply the formula, and you’ve got your key.

There are other scales too - the natural minor, the pentatonic, the blues scale, various modes - each with its own formula and its own sound. But the major scale is the reference point. Everything else is described in relation to it.

Triads

A chord is what happens when you play more than one note at the same time. Strum a guitar and you’re playing a chord - multiple notes ringing together.

A triad is a chord made of three notes, and it’s the simplest chord that tells you whether you’re in major or minor territory.

You build a triad by taking a scale and picking alternate notes: pick one, skip one, pick one, skip one, pick one. Take C major (C, D, E, F, G, A, B). Start on C, skip D, take E, skip F, take G. That gives you three notes: C, E and G - a C major triad. When you play a C major chord on guitar, you’re really just playing these same three notes doubled across different strings and octaves.

By the way — when you do this for every note in the major scale, playing all the notes with their thirds and fifths, it’s called the harmonised major scale. It gives you all the “legal” chords in a given key.

Those three notes are called the root, 3rd and 5th - just counting scale steps up from the starting note. C is the root, E is the 3rd, G is the 5th. What makes it a major triad is that the 3rd is a major 3rd (4 semitones from the root). Lower that 3rd by one semitone and you get a minor triad — like you get with D – F – A (the second chord in C major). Lower the 5th as well and you get a diminished triad, as you can see with the final chord above — B diminished (B – D – F).

There are three types of triad you’ll encounter:

• Major - root, 3rd, 5th (e.g. C-E-G)Sounds stable, bright.
• Minor - root, ♭3rd, 5th (e.g. C-E♭-G)Sounds darker, sadder.
• Diminished - root, ♭3rd, ♭5th (e.g. C-E♭-G♭)Sounds tense, unstable.

Which type you get depends on where the semitones fall in the scale. If you start on each note of the major scale in turn and do the same pick-one-skip-one recipe, you always get the same pattern: major, minor, minor, major, major, minor, diminished. That’s the harmonised major scale, and it’s the foundation of how chords work in a key.