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From triad to seventh chord: the logic of stacking thirds

A triad is built by stacking two thirds on top of a root: the first third, between the root and the middle note, gives the chord its third; the second, stacked on the first, gives the fifth. Each third can be major, four half steps, or minor, three half steps: a major triad stacks a major third then a minor third, a minor triad does the reverse. Either way, the total distance between the root and the fifth stays the same, seven half steps, a perfect fifth: what changes is only the position of the middle third.

A seventh chord adds a third stacked third, this time above the fifth, and the resulting note is called the seventh. That new third can also be major or minor, which places the seventh either eleven half steps above the root, a major seventh, or ten half steps above, a minor seventh. Crossing the type of triad, major or minor, with the type of seventh added, major or minor, gives the three families used most in practice: the dominant seventh, major triad plus minor seventh; the major seventh, major triad plus major seventh; the minor seventh, minor triad plus minor seventh. A fourth combination, minor triad plus major seventh, also exists under the name minor-major seventh, but it stays rare and falls outside the core trio this guide covers. Two further families, the half-diminished seventh and the diminished seventh, stack minor thirds instead of a classic major or minor triad: this guide introduces them briefly further down, with their full construction covered in the guide on suspended, diminished and augmented chords.

This table gives the identity card of each family on C, but the logic stays exactly the same on any root: just count the same intervals, in half steps, from the new starting note. It is this regularity, more than memorising twelve different chords per family, that lets you build any seventh chord in your head, without needing to look it up on an instrument.

The dominant seventh (7): the chord that demands its resolution

The dominant seventh pairs a major triad with a minor seventh: on C, that gives C7, made of C, E, G and Bb, the C major triad completed by a Bb sitting ten half steps above the root. In practice, the suffix 7 used on its own, with nothing else attached, always names this version: never the major seventh, which needs an explicit suffix, maj7 spelled out or a dedicated symbol, as this guide details further down.

What sets this chord apart from every other seventh chord is the interval between its third and its seventh: a tritone, six half steps, three whole tones exactly, the most unstable interval in the entire Western tempered system. On C7, that tritone links E and Bb. In classical tonal harmony, each of the two notes of the tritone carries an expected motion: the third, often close to the leading tone of the key, pulls up by a half step toward the root of the resolving chord, while the seventh pulls down by a half step toward the third of that same chord. On the move from G7 to C major, that gives B rising to C, and F falling to E: both notes of the tritone close in at the same time, each by a half step, which is why the ear hears this resolution as so natural, almost mandatory.

This engine of tension and resolution has a name, the V7 to I cadence, dominant to tonic, and it has shaped a large part of Western tonal harmony for centuries. The same logic also applies locally, inside a single piece, in the form of secondary dominants: a dominant seventh chord can briefly stand in for a diatonic chord to set up, for a moment, the resolution toward the next chord, before returning to the main key. This is the engine that makes the dominant seventh so common in blues, where it conventionally colours all three main degrees of the progression, including the tonic chord itself, as well as in jazz and pop, whenever a passage needs to push the movement toward the next chord.

The major seventh (maj7): the resting colour

The major seventh pairs the same major triad with a major seventh this time, not a minor one. On C, Cmaj7 gathers C, E, G and B, the seventh sitting eleven half steps above the root, just one half step short of the octave. That small gap changes the whole nature of the chord: with no tritone between the third and the seventh, none of the inner tension that forces a resolution remains, unlike the dominant seventh.

The result sounds stable, enveloping, a little suspended, with no urgency to go anywhere else: it is a chord that can settle on itself, at the end of a phrase, without feeling like an unfinished movement. That soft, almost dreamy colour has made the maj7 one of the harmonic signatures of modern jazz and bossa nova, where it very often serves as a resting chord, including as the tonic chord itself, a role the plain major triad used to hold alone in older harmony. It also shows up regularly in soft pop and ballads, whenever a song wants a richer harmony than a plain major chord, without tipping into the tension of a dominant seventh.

Functionally, the maj7 appears most often on the first degree of a major key, the tonic, and on the fourth degree, the subdominant: two spots where the plain triad is already stable, and where adding a major seventh only enriches the colour without changing the function. That is an important difference from the dominant seventh, which does change the function of the chord by adding a tension that was not present in the triad alone. A useful reference point for the ear: playing a maj7 right after a dominant seventh built on the same root is enough to hear the difference between the two colours, one tense, one at rest, even though only one note changes between them, the seventh itself, by a single half step.

The minor seventh (m7): the velvety sound, between colour and passing chord

The minor seventh pairs a minor triad, root, minor third, fifth, with a minor seventh. On C, Cm7 gathers C, Eb, G and Bb: the C minor triad completed by the same minor seventh, ten half steps above the root, as the dominant seventh, but sitting this time on a minor base rather than a major one.

That seventh softens the minor triad rather than darkening it further: the result sounds velvety and round, noticeably less dramatic than a plain minor chord on its own. It is one of the most used chords in soul, funk and jazz, where it plays two distinct roles depending on context: a colour role, when it serves as a resting chord on a minor first or sixth degree, and a passing role, when it sets up a move toward another chord.

That second role is especially common on the second degree of a major key, where the triad is naturally minor: there, the m7 becomes the first link in a three-chord progression widely used in jazz, the ii-V-I cadence, which the dedicated guide on that cadence covers in its own right, interval by interval and function by function. The sixth degree, also naturally minor in a major key, hosts an m7 the same way as a colour chord, often used as the starting point of a progression before moving to the second degree, then the fifth, then the tonic.

Why C7, Cmaj7/CΔ7/CM7 and Cm7/C-7: several notations for the same chord

The three families are told apart on a chart only by their suffix: 7 alone for the dominant, an explicit major marker for the major seventh, an explicit minor marker for the minor seventh. But unlike the suffix 7, which has been settled for a long time, the other two suffixes have been written in at least two or three different ways over time, and all four still coexist today on scores and charts that are otherwise recent.

For the major seventh, the Greek triangle, Δ, remains the most characteristic jazz notation, alongside maj7 spelled out and M7 as a capital letter on its own. Its precise origin is still debated, but period manuscripts offer solid clues: handwritten lead sheets by John Coltrane for the tunes Naima and Lady Bird, dated 1959, already use the triangle, as do Wayne Shorter's charts from around the same period, and Charles Mingus scores as early as 1957-1958 even use the combination -Δ7 to notate a minor chord with a major seventh. A commonly offered explanation holds that delta, the fourth letter of the Greek alphabet and the symbol for the digit four, was chosen because a major seventh chord is, at its core, a stack of four notes from the major scale. The triangle has the advantage of being visually unambiguous, which explains its lasting popularity in jazz, while pop and mainstream music mostly prefer maj7, clearer to read for a musician less versed in jazz jargon.

For the minor seventh, the same logic of clarity applies in reverse: alongside m7, common everywhere, jazz also uses a simple dash, C-7, to notate C minor seventh. That compact notation speeds up handwriting on a chart in the middle of a rehearsal, but it carries a well-known risk of confusion among musicians themselves: a dash can, on a quick read or a poor-quality photocopy, be mistaken for a minus sign or vanish altogether. It is partly this risk of confusion, between lowercase m and capital M, between a dash and a minus sign, that explains why so many teaching methods and notation software, including the Music Hub's Chords tool, now favour the spelled-out suffixes, maj7 and m7, slower to write by hand but noticeably safer to read in print or on screen.

Basic voicings on guitar

On guitar, the most direct way into a seventh chord starts from the barre shapes already known for triads. Starting from the E shape or the A shape, popularised by the CAGED system that the guide on barre chords covers at greater length, lifting or adding just one finger on the barre base is enough to turn a major triad into a dominant 7 or a maj7, or a minor triad into an m7: the hand position does not fundamentally change, only one note shifts inside the shape. It is the most economical way to add a whole vocabulary of seventh chords without learning four entirely new fingerings per chord.

Beyond these full barre shapes, jazz guitarists very often use lighter voicings, four notes across four adjacent strings, borrowed from an arranging technique called drop 2. The principle starts from a chord in close position, the four notes stacked as tightly as possible, then drops the second note from the top down an octave: the result spreads over a wider range, sounds more open, and above all sits more comfortably under the fingers on a guitar neck than the original close position. A variant, drop 3, applies the same principle to the third note from the top instead of the second. Popularised by jazz guitarists such as Joe Pass and Wes Montgomery, these drop 2 voicings remain the backbone of jazz guitar accompaniment today, whether for comping a chart or building a chord-melody arrangement.

These voicings stay generic tools, transposable onto any root and any progression: this guide deliberately fixes no position on any specific song, the goal being to understand the building principle well enough to apply it to any track in the catalogue.

Basic voicings on piano

On piano, the simplest approach to a seventh chord is called a shell voicing: rather than stacking all four notes of the chord, the left hand plays only the root, the third and the seventh, sometimes only the third and the seventh. That reduction does not weaken the chord: the third shows whether it is major or minor, the seventh shows whether it is dominant, major or minor, and those two notes alone are enough to identify the full harmonic colour without ambiguity. That was already the dominant approach among jazz pianists in the decades before the 1950s, when the left hand often played root and seventh while the right hand carried the melody and the tensions.

So-called rootless voicings push that logic a step further: developed in the 1950s by pianists such as Bill Evans, Wynton Kelly and Ahmad Jamal, they drop the root from the left hand altogether, relying on the fact that a bassist already plays it in a band context. The left hand is then free to play the third, the seventh and one or two extension notes, such as the ninth, for a richer, more modern sound than a plain shell voicing. Two basic positions structure this approach, distinguished mainly by the lowest note of the voicing: the position with the third below the seventh, and the position with the seventh below the third, the two alternating naturally as the chord changes along a progression, to keep hand movement to a minimum.

As with guitar, these voicings remain general templates, to be transposed onto any root: their teaching value lies precisely in working identically across all twelve keys, once the principle is understood for good.

The half-diminished and diminished sevenths: another family, in brief

Two more families of seventh chords build on a diminished triad rather than a classic major or minor one. The half-diminished seventh, notated m7b5, or sometimes with a slashed circle, ø7, adds a minor seventh, ten half steps above the root, to a diminished triad. The fully diminished seventh, notated dim7 or with a small superscript circle, °7, adds a diminished seventh to that same diminished triad, only nine half steps above the root, one half step less than an ordinary minor seventh.

That single half-step difference changes the geometry of the chord considerably: the diminished seventh actually stacks three strictly identical minor thirds, which makes the chord perfectly symmetrical. On C, Cdim7 and Ebdim7 share exactly the same four notes, as do Gbdim7 and Adim7: the same chord can therefore carry four different names depending on which note is treated as the root, a property classical composers and jazz arrangers have long exploited to modulate from one key to another almost without a seam. The half-diminished seventh, by contrast, stays asymmetrical like any other seventh chord, but it shares with the diminished the same instability that pushes toward a resolution, a bit like the tritone in the dominant seventh but with a different geometry; it notably became common in Western harmony during the 19th-century Romantic era, before fully entering jazz vocabulary in the 20th century.

Building these two chords in detail, hearing them, and spotting where they appear on a chart goes beyond the scope of this guide: the guide on suspended, diminished and augmented chords covers the diminished triad in its own right, the very foundation these two seventh chords build on.

Style contexts: where to hear each family

None of these three families belongs to a single style, but how often they show up varies a great deal from one genre to another. Jazz, from swing through bebop and beyond, leans on all three in close to equal measure: the dominant 7 to drive cadences forward, the maj7 to mark resting points, the m7 to fill the minor degrees of a progression and chain ii-V-I cadences. It is the style with the highest density of seventh chords per minute of music of any common genre, to the point where plain triads, without a seventh, become almost the exception rather than the norm.

Blues, and much of the rock that grew out of it, uses the dominant seventh in a particular way: it almost systematically replaces the plain major triad on the three main degrees of the progression, including the tonic chord itself, which runs against the classical logic where only the fifth degree naturally carries a dominant seventh. That usage gives blues its unmistakable colour, a little rough, never fully at rest even on the opening chord.

Soul and funk lean heavily on the m7 as the base chord of the accompaniment, often enriched with a ninth, for a round, groovy texture that still stays harmonically simple to the ear, without jazz's density of chords. Bossa nova, and much of Brazilian pop or soft international pop, lean the other way, giving the maj7 pride of place for that suspended colour already described above, which suits a moderate tempo and an unhurried melodic line particularly well. Mainstream pop, meanwhile, uses all three families sparingly, in small touches, to enrich a progression here and there while keeping it built mostly around plain triads, rather than making them, as jazz does, the basic harmonic material of every bar.

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