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Decoding the letter: international notation

On a chart, every chord starts with a capital letter that names its root in international notation, also called the English system. The mapping is fixed: A, B, C, D, E, F, G run straight up the alphabet. A C chord is written C, a G chord is written G. The letters start at A because English notation begins on the note A, whereas the French scale is recited from Do (C).

The handiest anchor for the whole table is that the letters simply follow alphabetical order: fix one in your mind and the rest fall into place from there. Once that table is set, half the reading is done: the letter always tells you the base note of the chord, and everything that comes after only spells out its colour.

Reading the base suffixes of a chord

A chord symbol reads like a recipe. By default, a lone letter (C, G, D) means a major chord, built on the root, its major third and its fifth. Anything attached to the letter alters that starting triad. A lowercase m (Am, Em, Dm) lowers the third by a half step to give a minor chord: only the third changes between major and minor, yet the mood swings from bright to dark. The figure 7 (C7) adds a minor seventh and marks the dominant seventh chord; maj7 instead adds a major seventh with a softer sound, a note sitting eleven half steps above the root.

Other suffixes follow the same logic of alteration. A suspended chord (sus4) replaces the third with the fourth above the root, and sus2 replaces it with the second: with no third, the chord is neither major nor minor, it stays in suspense. The labels dim (diminished) and aug (augmented) alter the fifth, lowered or raised respectively. Finally, a slash chord like C/E forces a bass note: the part to the left of the slash is the chord played, the note to the right is the lowest note to sound. C/E therefore reads as C major with an E in the bass.

Going further: 9th, 11th and 13th chords

Beyond the seventh, the same logic keeps going: you stack yet more thirds on top of the chord. After the root, third, fifth and seventh comes the ninth, a third above the seventh, then the eleventh, another third up, then the thirteenth. These three degrees are nothing more than the 2nd, 4th and 6th of the scale played an octave higher: the ninth is the 2nd degree bumped up an octave, the eleventh is the 4th degree bumped up an octave, the thirteenth is the 6th degree bumped up an octave. A ninth chord like C9 stacks root, third, fifth, minor seventh and ninth: C, E, G, B♭, D. An eleventh chord like C11 adds the eleventh on top: C, E, G, B♭, D, F. And a thirteenth chord like C13 goes all the way to the thirteenth: C, E, G, B♭, D, F, A — seven stacked notes in theory, the tallest tower commonly built on a chord.

These extensions are not reserved for some esoteric style: they are the daily bread of jazz, where a 9th or 13th chord colours the smallest cadence, of funk and soul, where a 9 or 11 chord over a groovy bass line gives that unmistakable suspended flavour, and of piano ballads in the R&B or gospel vein, where a plain major chord gains depth as soon as a ninth is added. There is nothing exotic about the logic: they are just triads or seventh chords with one or more extra colours stacked on top, degree by degree, always in thirds.

The add9 versus 9 trap: two chords people mix up constantly

This is the most common mix-up as soon as a chart shows a number after the letter: add9 and 9 look alike but name two different chords, with a different number of notes. An add9 chord, like Cadd9, adds only the ninth to the base triad, without touching the seventh: C, E, G, D, in other words the major triad plus a ninth, four notes in total. A ninth chord, like C9, instead implies the whole stack underneath: the triad, the minor seventh, and the ninth on top: C, E, G, B♭, D, five notes in total. The difference comes down to a single note, the minor seventh, yet it completely changes the colour: add9 keeps a clean, open sound close to the starting triad with just a touch of colour, while C9 sounds more tense, more dominant, pulled toward resolution.

The rule to remember fits in one sentence: the word add isolates a single note added to the triad, nothing more, whereas a bare number after the letter always calls up the whole chain of sevenths underneath it. A C9 therefore implies a minor seventh even though it is not written in the name, exactly as a C13 implies a seventh, a ninth and an eleventh beneath the thirteenth, unless stated otherwise. A maj9 chord (Cmaj9) follows the same rule but with a major seventh: triad plus major seventh plus ninth, that is C, E, G, B, D. When in doubt in front of a chart, the reflex is simple: if the word add appears, only one note is added; otherwise, the number pulls in the whole stack beneath it.

What you actually play: the notes you can leave out

On paper, a thirteenth chord lines up seven different notes. In reality, nobody plays all seven on a single harmonic instrument: a piano hand or a guitar grip simply does not have enough fingers, and the result would sound thick and muddy rather than rich. In practice, the root is commonly left out, especially if a bass player or a bass line already covers it elsewhere, along with the plain fifth, the least characteristic note of the chord: it adds almost no colour of its own, unlike the third or the seventh.

What almost always stays are the guide tones: the third, which tells you whether the chord is major or minor, and the seventh, which tells you whether it is dominant or maj7-type. These two notes alone are enough to make the chord's quality recognisable by ear. On top of them comes the extension called for by the chord name, the ninth, eleventh or thirteenth, the one that gives its particular colour. On an 11th or 13th chord built on a dominant seventh, the third and the eleventh actually clash easily; many musicians then drop one or the other, depending on the sound they are after. A C13 played in practice can therefore shrink to four notes, E, B♭, D and A — third, seventh, ninth and thirteenth —, and sound just as convincing as a theoretical seven-note C13. What looked complex on paper becomes a handful of well-chosen notes to the ear.

This table will not replace your ear, but it gives a quick reference, suffix by suffix, for what changes compared with the starting triad.

The bar, the box and the beats

A chart is split into boxes, separated by vertical bar lines. A box is the space between two bar lines, and it usually stands for one bar. Since songs are very often in 4/4, each box then holds four beats. You read the boxes left to right, then drop to the line below, exactly like text.

What sits inside the box tells you how long each chord lasts. A single chord in a bar means it fills the whole bar, all four beats in 4/4. When several chords share one box, a diagonal slash or subdivisions split the beats between them: two chords side by side in a four-beat bar often take two beats each. It is this layout that shows you where the chord changes will land.

Repeats and navigation in the chart

A chart avoids rewriting everything thanks to a few repeat signs. The percent sign placed in a box means repeat the previous bar: instead of copying the chord name again, you drop in this shorthand and play the same thing. It comes up often when one chord holds across several bars in a row.

For whole sections, repeat bar lines mark the path. A repeat bar line is a bar line with two dots: the dots on the right mark the start of the part to repeat, the dots on the left mark its end. A note like x2 or x3 tells you how many times to play the stretch concerned. By spotting these signs before you start, you know in advance when a part loops and where the thread of the song comes back.

The Nashville Number System: the chart without letters

There is another way to write a chart, very common in professional studios, particularly in the United States within the Nashville session-musician scene: replace the letters with degree numbers. Instead of writing C, F, G, you write 1, 4, 5, the numbers matching the position of each chord in the scale of the song's key. This notation is known as the Nashville Number System. A theoretical progression such as I-V-vi-IV, in roman-numeral harmony-textbook fashion, would be written for instance as 1 5 6- 4 in this notation, the minus sign marking a minor chord on the sixth degree.

The system was born in the late 1950s, around 1957, when Neal Matthews, a singer in the vocal group The Jordanaires, worked out a way to write vocal parts in numbers so the group could get through several recording sessions a day without memorising everything by heart, drawing on the shape-note systems used by gospel quartets in the 1930s and 1940s. In the early 1960s, musician Charlie McCoy picked up this approach and extended it to chords and the rhythm section for studio musicians, who often had to sight-read an entire song on first hearing a demo. The system was later formalised and published as a book by Chas. Williams in 1988.

The practical payoff fits in one sentence: since the numbers stand for degrees relative to the key rather than fixed notes, the same number chart can be played in any key without being rewritten. A singer who changes key from one night to the next simply calls out the new starting key, and the musicians transpose on instinct while reading the same numbers. It is a notation built for speed and the ear-memory of session musicians, complementary to the letter chart this guide covers, but built on exactly the same logic of degrees as reading a classic chord chart.

The structure of the song, and what the chart leaves out

Beyond the chords, a chart follows the structure of the song, that is the order of its sections. The intro brings the song in, the verse tells the story and changes its words each time round, the chorus comes back unchanged and carries the main message, the bridge creates a break with chords different from the rest, and the outro closes it out. A very common pop form runs verse, chorus, verse, chorus, bridge, chorus, sometimes summed up as ABABCB.

One essential point remains: the chart shows the harmonic sequence, which chords and when to change, but not the exact rhythm nor how to play each chord, whether it is written in letters or in Nashville numbers. The melody isn't there either, which makes it ideal for accompaniment but assumes you already know the tune. For the rhythm and the exact placement, you lean on your ear and your memory of the song. In the Music Hub, every chart comes with the key, the suggested capo and a piano to hear each chord, enough to fill in what the chart alone doesn't say.

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