Chords and Progressions

A chord is a set of notes sounded together and heard as one event rather than as separate voices. A progression is chords arriving in an order and going somewhere. Nearly every song you know is a handful of chords looping in a fixed sequence — while a melody moves across the top of them.

Players tend to treat chords as shapes: things the hand does, named by somebody else, picked by a songwriter out of all the chords there are. Two of those three are wrong. A key hands you seven chords and most songs never leave them — and the shapes came second, worked out by people hunting for notes a scale had already picked.

Skip Every Other Note and the Scale Builds Its Own Chords

Take the major scale and its step pattern as given. Start on any degree and take every other note — that one, skip, the next, skip, the next. Three notes with a gap between each is a triad, and it is where nearly every chord you play comes from.

Do that from all seven degrees and you have the seven chords of the key. They do not come out the same. The scale's steps are uneven, so the gaps depend on where you started: sometimes four semitones then three, which is a major triad, sometimes three then four, which is minor, and once — exactly once — three then three, which is diminished. The order is fixed for every major key: major, minor, minor, major, major, minor, diminished.

The third is what switches a chord between major and minor, and the last lesson made that point. What it had no reason to say is what the two share: seven semitones from root to top, the fifth you already know as the hollow one. That is the floor under both. The diminished triad is the one place in the key where the floor goes — two stacked minor thirds leave root and top six semitones apart, a tritone, and nothing is holding the chord up. On its own it sounds like a question with the answer cut off, and you will meet it lodged inside other chords more often than you strum it.

Roman Numerals Are What Make a Progression Portable

Number the degrees one to seven and write the chord built on each as a roman numeral — uppercase where the triad came out major, lowercase where it came out minor, a small circle on the diminished one. I, ii, iii, IV, V, vi, vii°. That is the convention in English-language teaching and most popular-music writing, and the one used here, but not the only one going: some traditions capitalise every degree and mark quality separately, so check what a book is doing before you trust its lowercase.

The payoff is worth more than it looks. A numeral names a job, not a note, so writing a song down as I–V–vi–IV writes it down in all twelve keys at once. In D that is D, A, Bm and G; move it up two frets and it is E, B, C♯m and A, chart unchanged. Transposing for a singer who cannot reach the top note stops being a rewrite — what you wrote down was never the notes.

Session players formalised the same idea as the Nashville Number System, using Arabic numerals and marking minor chords with a dash or a small m, because a singer dropping the key mid-session should not cost anybody a new chart. Leonard Cohen's "Hallelujah" reads its own chart out loud. It sits in C, and the line about the fourth, the fifth, the minor fall and the major lift arrives over F, G, A minor and F — IV, V, vi, IV, in that order.

The Same Few Progressions Recur, and Only Half the Reason Is Musical

Start with what is genuinely mechanical. A major key contains only three major triads — I, IV and V — and between them they use every note in the scale. In C that is C–E–G, F–A–C and G–B–D, which accounts for all seven. A song can spend its whole length on three chords and never sound like it left the key, because it never did.

V pulls the hardest, and the pull is physical rather than conventional. Its third is the seventh degree of the scale, the note that already leans toward home; add a seventh to the chord and it contains a tritone, six semitones between the third and the seventh — B against F inside a G7. Both notes sit one semitone from somewhere stable, so B climbs to C, F drops to E, and with them the whole chord resolves. IV pulls the other way, since I is the V of IV. And vi is the cheapest colour change in the key: it shares two of its three notes with I, so a whole shift of mood costs one note of movement.

Now the honest half. None of it explains why one particular four chords dominates a given decade. Ergonomics do some of the work — the chords that fall under a guitarist's hand in open position keep turning up — and imitation does the rest, because every player learns from records made by players who learned from records. Treat any claim that a precise percentage of songs uses a given progression with suspicion; those figures circulate endlessly and almost never arrive with a corpus behind them. You can hear the recurrence without counting it. U2's "With or Without You" loops four bars of D, A, Bm and G under the entire song. The twelve-bar blues is a fixed grid: four bars of I, two of IV, two of I, then V, IV and two of I. Jazz runs on ii–V–I, three roots stepping up a fourth each time to land on home.

Which Note Sits in the Bass Is a Separate Decision

Which of a chord's notes ends up lowest is a second choice, and it changes what the chord does. Root in the bass is root position, and it sounds planted. Put the third down there — first inversion — and the chord gets lighter and less final: useful mid-phrase, weak as an ending. Put the fifth down there and you have second inversion, where bass and root sit a fourth apart, an interval the older tradition treated as a dissonance needing resolution. It still sounds like something in transit.

Charts write these as slash chords, so C/E is a C major triad with E in the bass — on guitar, often just which string you start the strum from. What you buy is a bass line. Four chords all in root position give a bass that jumps; invert one or two and it walks down by step instead, turning the low end into a melody rather than a run of landings. Procol Harum's "A Whiter Shade of Pale" is built on that, a bass descending stepwise under the whole song, borrowed from music two centuries older.

Sevenths Are One More Note Up the Same Stack

Keep going. Skip another degree above the fifth and every triad in the key becomes a seventh chord with no new machinery involved — major sevenths on I and IV, minor sevenths on ii, iii and vi, a dominant seventh on V alone. The seventh degree gives a half-diminished: the diminished triad plus a seventh, and that fourth note quietly hands the chord a perfect fifth it did not have, taking some of the edge off.

The extra note stops a chord sounding like a conclusion. A major seventh floats, a minor seventh turns conversational, and a dominant seventh is unstable in the specific direction described above — which is why V7 is the standard way to make a return home feel inevitable. Jazz and soul are largely written in sevenths because plain triads are too definite for music that has to keep moving. Blues does something else again and puts dominant sevenths on all three chords at once, so everything is pulling and nothing quite arrives.

What to Do With This on the Instrument

• Write songs down as numerals, not letters — I–V–vi–IV is the same chart in every key, so transposing for a singer stops being a rewrite.
• Build the key before guessing at a chord — stack thirds off each degree and you have the seven it is probably using; anything else is an event.
• Reach for vi when a section needs darkening — it shares two notes with I, so the change of mood costs you one note of movement.
• Put the seventh on V and leave the rest alone — one dominant seventh makes a plain progression pull; sevenths on everything is a genre decision, not a default.
• Treat the bass note as its own choice — the same four chords with one inverted turn a jumping bass into a line that walks down by step.
• Learn the tritone by ear — sound the third and seventh of a dominant chord, then let them resolve outward; that is most of what a cadence is.