Chords are stacked intervals, nothing more

Take a note, skip a letter, take the next one. Every chord you will ever play is built with that one move, repeated.

A chord is three or more notes played together. That much is obvious from hearing one. What is less obvious — and what makes every chord name suddenly readable — is how they are built.

This is step five of the music theory path. It assumes you know what intervals are, because chords are made of them.

Chords are stacked thirds. Take a note, skip a letter, take the next one, skip another letter, take that one. Three notes, and you have a chord.

The triad

Those three notes have names. The one you started on is the root — it gives the chord its letter. The middle note is the third. The top note is the fifth. Root, third, fifth. Every basic chord you will ever play is some version of these three.

A three-note chord like this is called a triad, and there are only four kinds. The difference between them is which sort of third goes where.

Major and minor differ by one note

This is the single most useful fact in harmony. C major is C, E and G. C minor is C, E flat and G. The root is the same. The fifth is the same. The only thing that changed is the middle note, moved down by one semitone.

One semitone is the entire emotional distance between bright and dark in Western music. Try it on your instrument — play a major chord, drop the middle note a fret or a key, and listen to what happens.

Everything else about the chord is unchanged. That is worth sitting with, because it tells you the third is the note carrying the character, and the root and fifth are structure.

Adding a fourth note

Keep stacking thirds and you get a seventh chord. Root, third, fifth, seventh — four notes instead of three.

Sevenths are where chords stop sounding like textbook examples and start sounding like music. A plain C major is stable and a little plain. A C major seventh is warm and slightly wistful. A C dominant seventh is restless and wants to move somewhere.

That restlessness is not a metaphor. The dominant seventh contains a tritone, the most unstable interval there is, and the ear genuinely wants it resolved. It is the engine that drives most chord progressions home.

Inversions

You do not have to play the root at the bottom. C E G is the same chord as E G C or G C E — the same three notes, reordered. These are called inversions.

This matters practically more than theoretically. Inversions are how you move between chords without your hand jumping around the instrument, and how a bass line moves independently of the harmony above it.

Chords belong to keys

Chords are not free-floating. Build a triad on each note of a major scale using only notes from that scale, and you get seven chords — three major, three minor, and one diminished, always in the same order.

In C major those are C, D minor, E minor, F, G, A minor, and B diminished. Those seven chords are the vocabulary of that key, and most songs in C use very few notes outside them.

This is what the circle of fifths is showing you when it displays a key. And it is why a chord can belong to several keys at once — the overlap between keys is exactly what makes changing key possible.

What to do with this

Learn the four triad types by their interval recipe rather than by memorising shapes. Four plus three is major, three plus four is minor. Once that is automatic, you can build any chord on any instrument without looking anything up.

Then use the chord finder to check yourself. Pick a root, pick a quality, work out the notes in your head first, then look.

Next: progressions — why chords move where they move.

What is an interval in music?

An interval is the distance between two notes. It gets measured two ways at once, which is the only reason it seems complicated.

An interval is the distance between two notes. That is the entire definition, and if it were left there, nobody would find intervals difficult.

This is step three of the music theory path. It assumes you can read notes on a staff and count rhythm — steps one and two.

The difficulty comes from the naming. Every interval is measured two different ways at the same time, and both measurements end up in its name.

The number counts letter names

Start on the lower note and count letter names up to the higher one, including both ends. C to E is C, D, E — three letters, so it is some kind of third. C to G is C, D, E, F, G — five letters, so it is some kind of fifth.

This is why the counting feels wrong at first. C to D is a second, not a first, because you count the note you started on. There is no interval called a first; the same note twice is a unison.

The quality counts semitones

The letter count alone is not enough, because thirds come in two sizes. C to E spans four semitones. C to E flat spans three. Both are thirds by letter count, but they sound completely different — one bright, one dark.

So each interval gets a quality as well as a number. Seconds, thirds, sixths and sevenths are either major or minor, one semitone apart. Fourths, fifths and octaves are called perfect.

Why some intervals are called perfect

The perfect intervals are the ones where the two notes vibrate in the simplest mathematical ratios — two to one for an octave, three to two for a fifth. They sound so consonant that they barely register as two separate notes. They do not come in major and minor versions; instead they can be widened to augmented or narrowed to diminished, which happens far less often.

You do not need the physics. You need to know that fourths, fifths and octaves behave differently from everything else.

The full list

Twelve semitones, twelve intervals, then it repeats an octave higher. This is the whole system:

Why any of this matters

Intervals are not a topic you study and then move past. They are the material everything else is made of.

Chords are stacked intervals. A major chord is a major third with a minor third on top of it. Change the lower third to a minor third and you have a minor chord. That is the only difference between the two.

Scales are patterns of intervals. A major scale is a fixed sequence of whole and half steps — two, two, one, two, two, two, one. Start that pattern on any note and you get that note’s major scale. The pattern is the scale; the starting note is just where you put it.

Keys relate to each other by interval. The circle of fifths is called that because each step around it is a perfect fifth. It is one interval, applied twelve times.

How to actually learn them

Do not memorise the table. Learn to hear three of them first: the octave, the perfect fifth, and the major third. Those three are the skeleton of nearly all Western harmony, and once you can pick them out, the others sit in relation to them.

Play two notes on your instrument, name the interval, then check. A few minutes a day beats an hour once a week, because this is recognition rather than understanding — and recognition only comes from repetition.

Next: chords, which are what happens when you stack these on top of each other.

Key signatures: what those sharps at the start mean

Those sharps at the start of a piece exist for one reason: to save you writing the same accidental forty times.

At the start of a piece, just after the clef, you will often see a cluster of sharps or flats. That is the key signature, and it exists for one reason: to save ink.

This is step four of the music theory path. It assumes you can already read notes on a staff.

What it is actually doing

If a piece is in the key of D, almost every F in it will be an F sharp and almost every C will be a C sharp. Writing a sharp symbol next to every single one would be exhausting to write and exhausting to read.

So instead you declare it once. Two sharps at the start, positioned on the F line and the C space, and from then on every F and every C in the piece is sharp unless something says otherwise.

The order is always the same

Sharps always appear in this order: F, C, G, D, A, E, B. Flats appear in exactly the reverse: B, E, A, D, G, C, F.

This is not arbitrary and it never varies. A piece with three sharps has F sharp, C sharp and G sharp — always those three, never a different combination. Once you know the order, counting the symbols tells you exactly which notes are affected.

Working out the key from the signature

For sharps, look at the last sharp in the signature and go up one semitone. Three sharps ends on G sharp, so the key is A major.

For flats, look at the second-to-last flat. That is the key. Three flats gives you E flat major. The one exception is a single flat, which is F major — worth simply memorising.

Major or minor?

Every key signature serves two keys, one major and one minor. Two sharps is either D major or B minor. The signature alone cannot tell you which.

The music tells you. Look at which chord the piece starts and ends on, and listen to whether it sounds bright or dark. That is usually enough.

Time signatures explained without the math

A time signature looks like a fraction and is taught like one. It is not. It is two separate instructions stacked up.

A time signature looks like a fraction and is taught like one, which is why so many people find it confusing. It is not a fraction. It is two separate instructions stacked on top of each other.

This is step two of the music theory path. Step one, reading the staff, is worth doing first if you have not.

The top number: how many

The top number tells you how many beats are in a bar. If it says 4, you count to four and start again. If it says 3, you count to three. That is genuinely all it does.

This is the number you can hear. Put on almost any pop or rock song and count along — one, two, three, four, one, two, three, four. You will find the pattern within a few seconds without knowing anything about notation.

The bottom number: what kind

The bottom number tells you which kind of note gets one beat. A 4 means a quarter note. An 8 means an eighth note. A 2 means a half note.

This is the part that trips people up, because it feels like it should change the speed. It does not. Tempo controls speed. The bottom number only decides which note value you are calling a beat.

Why 6/8 feels different from 3/4

Both have six eighth notes in a bar. On paper they look almost interchangeable. In practice they feel nothing alike, because of where the emphasis falls.

In 3/4 you feel three strong beats: ONE two three, ONE two three. Think of a waltz. In 6/8 you feel two groups of three: ONE two three FOUR five six. Think of a jig, or a slow blues shuffle.

Same notes on the page, completely different music, and the only thing telling you which is which is the time signature.

The practical takeaway

When you see a new time signature, ask two questions in order. How high do I count? And what am I counting? Everything else follows from those two answers.

Count out loud while you play. It feels ridiculous and it works better than anything else.

What the circle of fifths is actually for

Everyone shows you the wheel. Almost nobody tells you the three questions it answers faster than working them out.

Every music theory book has the same picture: a clock face with letters around the edge. C at the top, G to its right, then D, then A. Most explanations stop there, as if the diagram explains itself. It does not.

This is step six of the music theory path. If terms like key signature or diatonic are new, the earlier steps cover them first.

The circle of fifths is a lookup table. It answers three questions faster than working them out from scratch, and once you know which three, the picture stops being decoration and starts being useful.

Why the notes are in that order

Start on C and count up five letter names — C, D, E, F, G. You land on G. Do it again from G and you land on D. Keep going and you eventually pass through all twelve notes and arrive back at C. That is the whole construction. The circle is just that walk, drawn as a loop.

What makes it useful is that each step adds exactly one sharp to the key signature. C has none. G has one. D has two. Going the other way, counterclockwise, each step adds a flat instead.

The three things it tells you

First, key signatures. Count the steps from C and you have the number of sharps or flats. No memorisation required.

Second, the chords that belong to a key. The chord you are on, plus its two neighbours, are the three major chords of that key. The three notes sitting directly inside them on the inner ring are the minor chords. That is six of the seven chords in any key, read straight off the diagram.

Third, which keys sound close to each other. Keys that sit next to each other on the circle share almost all their notes, which is why moving between them sounds smooth and moving across the circle sounds abrupt.

When you would actually reach for it

Writing a song and want a chord that will sound unexpected but not wrong? Take one step around the circle. Trying to work out why a piece modulates where it does? Find both keys on the circle and look at the distance. Learning scales and want an order that builds on itself? Follow the circle rather than going alphabetically.

The diagram is not the lesson. The walk in fifths is the lesson, and the diagram is just a convenient way to keep it in front of you.