How Chords Work

Every chord starts with a scale

A chord is not a random handful of notes that happen to sound nice together. It is built by a rule, and the rule is boringly simple: take a scale, start on a note, and stack every other note. Play C, skip D, play E, skip F, play G — and you have a C major chord. Do the same starting from D and you get D, F, A, which is D minor. The pattern never changes; only where you start it does.

Stacking in alternate scale steps means each pair of notes is a third apart, and thirds are the interval Western harmony is built on. Two notes stacked in thirds give you a triad, three give you a seventh chord, four give you a ninth. That is the entire architecture. Everything from a folk song's three chords to a jazz standard's dense voicings is the same operation, repeated more or fewer times.

This is why chords and scales are not separate topics that you learn one after the other. They are two views of the same material: a scale is the notes laid out in order, a chord is the same notes stacked up. Once you see that, learning a new key stops being memorisation and becomes arithmetic. Thechord findershows the stack for any chord you pick, with each note labelled by the interval it contributes.

Major or minor comes down to one note

A triad has three notes: the root, the third and the fifth. The root names the chord and the fifth is nearly always seven semitones above it, doing very little except adding weight. Almost all of the emotional character lives in the third.

Count semitones from the root and the difference is stark in how it sounds but tiny in size. A major third is four semitones; a minor third is three. One semitone — one fret, one piano key — is the entire distance between "bright and settled" and "sad and inward". It is the most efficient emotional switch in music, and it is why on guitar the shapes for E and Em, or A and Am, differ by a single finger.

The suspended chords are worth a moment. They replace the third with the note below or above it, which removes the very thing that decides major or minor. The result sits in limbo and strongly wants to move — which is exactly why a sus4 resolving to a plain major chord is one of the most satisfying two-chord moves in popular music.

The seven chords of a key

Apply the stacking rule to every note of a major scale and you get seven chords, and their qualities always fall in the same order. In any major key: I major, ii minor, iii minor, IV major, V major, vi minor, vii diminished. Capital numerals are major, lowercase are minor. In C that gives C, Dm, Em, F, G, Bdim.

This pattern is fixed. It does not change with the key, which means once you learn it in C you know it everywhere — the chords of G major are G, Am, Bm, C, D, Em, F♯dim, and the relationships between them are identical. Songwriters lean on this constantly: pick a key, and these seven chords are guaranteed to sound like they belong together because they are all drawn from the same seven notes.

Three of them do most of the work. The I is home. The V creates the strongest pull back to home, because it contains the leading note a semitone below the tonic. The IV is a gentle step away that resolves comfortably in either direction. Add the vi — the relative minor, which shares two of its three notes with the I chord — and you have the four chords behind an extraordinary share of recorded music.

Why progressions feel like they are going somewhere

The famous I – V – vi – IV works because of what happens between the chords, not what is in them. You start at home, move to the chord with the most tension, sidestep the expected resolution into the relative minor — which feels like a surprise but uses almost the same notes as home — and then land on IV, which leans back toward the tonic and sets up the loop again. It never fully closes, which is precisely why it can repeat for four minutes without becoming tedious.

Compare that with ii – V – I, the backbone of jazz. Here every step tightens: ii sets up V, V is maximally unstable, I resolves it completely. It is a full stop rather than a loop, which is why it usually appears at the end of a phrase rather than underneath a whole song.

Notice rows one and four: the same four chords in a different rotation produce a completely different mood. Starting on the minor chord makes the whole loop sound melancholy even though not a single note has changed. Order is doing the emotional work, which is a genuinely useful thing to know when a song you are writing feels close but wrong.

Sevenths and beyond

Add one more third on top of a triad and you get a seventh chord — four notes instead of three, and considerably more colour. The distinction that trips people up is between the two kinds. A major seventh (Cmaj7: C E G B) adds the natural seventh, a semitone below the octave, and sounds warm, dreamy, slightly unresolved in a pleasant way. A dominant seventh (C7: C E G B♭) flattens that note, and the result is restless and bluesy — it actively wants to move somewhere.

That restlessness has a cause. A dominant seventh contains a tritone, the interval three whole tones wide that was considered so unstable that medieval theorists nicknamed it the devil in music. In a ii–V–I the tritone inside the V7 chord resolves outward into the tonic, and that resolution is the strongest gravitational pull in tonal harmony. It is why blues built almost entirely on dominant sevenths feels perpetually in motion.

A minor seventh (Cm7: C E♭ G B♭) is the smooth, unhurried one — the sound of soul and neo-soul verses. Beyond sevenths you keep stacking: ninths, elevenths and thirteenths add successively more colour and successively less stability. In practice guitarists and pianists drop notes from these larger chords, because six strings and ten fingers run out before the theory does; the fifth is usually the first to go, since it contributes least.

Inversions and voicings

A chord is defined by which notes it contains, not by their order or octave. C E G, E G C and G C E are all C major. Rearranging them changes the inversion, and while the chord's name stays the same its character shifts noticeably: root position sounds solid and declarative, first inversion (third in the bass) feels lighter and more mobile, second inversion (fifth in the bass) sounds unsettled and usually wants to move on.

The practical value is voice leading. If you play C then F in root position, your hand jumps and the two chords sound like separate events. Play C in root position and F in second inversion and only one note has to move, so the change sounds smooth and connected. Good accompaniment is largely the craft of choosing inversions so that individual notes move as little as possible.

Guitar makes this visible. Every shape in the chord finder is a different voicing of the same chord — the same notes in a different order and register, some with notes doubled at the octave. That is why an open C and a barre C at the eighth fret sound recognisably like the same chord and yet noticeably different in weight and brightness.

Reading a guitar chord diagram

Chord boxes look cryptic for about thirty seconds. The vertical lines are strings, with the lowest-pitched (thickest) on the left. The horizontal lines are frets. A dot shows where to press. Above the diagram, × means do not play that string at all, and ○ means play it open with nothing pressed.

A thick bar across the top is the nut, meaning the shape sits at the very start of the neck. When there is no nut, a number beside the diagram tells you which fret the top line represents — that is how a movable shape gets written once and reused all over the neck. A long rounded bar across several strings is a barre: one finger flattened across them all, which is the technique that makes those movable shapes possible in the first place.

The reason barre chords matter so much on guitar is that the instrument has no open strings above the nut. Move an open E major shape up two frets and the strings that used to ring open now have nothing holding them at the right pitch, so the index finger takes the nut's job. Learn two shapes — the E-shape with its root on the sixth string and the A-shape with its root on the fifth — and you can play every major and minor chord in existence by sliding them to the right fret.

Working backwards from notes to a name

Sometimes you have the notes and want the name — you worked something out by ear, or you are staring at a bass line and a melody and want to know what the harmony is. The method is mechanical. Reduce the notes to pitch classes, ignoring octaves and duplicates. Try each one as a candidate root, measure the intervals from it to the others, and see whether they match a known pattern.

Usually one candidate produces a recognisable shape and the others produce nonsense, and that one is your chord. Sometimes several fit, which is not a failure of the method — it is a real ambiguity in the music. A diminished seventh is the classic case: its four notes are spaced exactly three semitones apart, so it is perfectly symmetrical and any of the four can legitimately be heard as the root. Composers exploit this to pivot between distant keys, since the same four notes can be spelled four different ways.

The chord finder's "Name my notes" mode does exactly this search. Click the notes you have and it lists every standard chord that matches, ordered so the reading with your lowest note as the root comes first — which is nearly always the one you meant.

Putting it to use

Theory earns its keep when it stops being a list of facts and turns into a set of moves. Three worth trying immediately. First, when a progression feels flat, swap one chord for its relative minor or major — replace IV with ii, or vi with I — and hear what changes. Second, if a section sounds too plain, upgrade a triad to a seventh; maj7 on the I chord instantly sounds more sophisticated, and a dominant 7 on the V makes the resolution stronger.

Third, and most useful of all, learn the numbers rather than the letters. If you think of a song as I–V–vi–IV rather than C–G–Am–F, you can play it in any key by moving the same pattern, transpose instantly for a singer, and recognise the same progression when it turns up in a completely different song. Every musician who seems to pick things up impossibly fast is doing this.

Open thechord finder, pick a key, and click through its seven diatonic chords while listening to each one. Then try the same seven in a different key and notice that the feeling of each degree is identical even though every note has changed. That single exercise teaches more about how harmony works than a chapter of reading, and once it clicks you can play these on thevirtual pianoto hear how they connect.