What a Seventh Does to a Chord (and When to Leave It Alone)

A triad is three notes: a root, a third, a fifth. It is stable, settled, complete in itself. C major is C, E and G, and you can sit on it all day. A seventh chord adds one more note, the seventh degree of the scale, stacked on top. That single addition changes the chord's posture. Where the triad stood square, the seventh chord leans, and the interesting part is that the three common sevenths lean in three different directions.

Femi rang on Tuesday to reopen an argument about a chord substitution we technically settled in 1998, and we ended up, as we always do, back at the sevenths. So this seems a good week to walk through them, patiently, one at a time.

The dominant seventh, which wants to move

Build a seventh on the fifth degree of the key and you get the dominant seventh. In C major that is G, B, D, F: a G major triad with an F added on top. Have a listen. Play it, and then sit there and try not to play anything next. You will find it almost impossible. The chord is asking a question, and the question has a fairly insistent tone.

The reason is two of its notes: the B and the F. They are a tritone apart, the most restless interval we have, and that pair behaves like a stretched spring. The B wants to rise a semitone to C; the F wants to fall a semitone to E. Let them both go where they are leaning and you land, neatly, on a C major chord (C and E sit right there waiting). That is why a dominant seventh feels like it is going somewhere: it genuinely is. The lean is built into the notes.

The major seventh, which wants to stay

Now build a seventh on the home chord itself. C major seventh is C, E, G, B. It sounds, to most ears the first time, soft and a little wistful; the word people reach for is usually "dreamy". Have a listen to that one too, and notice that it does not push you anywhere. It is content.

The note doing the work is the B, sitting a semitone below the root C. In the dominant chord the tension pulled outward, toward resolution. Here the rub between the B and the C is gentle, and it stays at home; it colours the chord without demanding you do anything about it. A major seventh is the sound of a happy memory you are standing just inside of, rather than just outside. It is worth knowing that the two chords are built the same way, a triad plus a seventh, and yet one strains at the lead while the other lies down by the fire.

Built the same way, a triad plus a seventh, and yet one strains at the lead while the other lies down by the fire.

The minor seventh, the easy companion

The minor seventh (in C, that would be C, E flat, G, B flat) is the most even-tempered of the three. It takes the slight melancholy of a minor triad and rounds its edges, softens it, makes it conversational. You will hear it all over the calmer corners of soul, jazz and folk, very often sitting in the middle of a progression where it neither announces an arrival nor demands a departure. It travels well. It is the chord you can put almost anywhere and trust to behave.

A note from the kitchen

Here is where I should say the thing I most want you to take away, because it is the part people skip. A seventh is salt in a sweet recipe. Used once, in the right place, it makes everything around it taller; the contrast is the whole point. Used on every chord, indiscriminately, it stops being contrast and becomes the flavour of the whole thing, and then you taste nothing else. I have made that loaf. It is edible and it is boring.

So the genuinely useful question is rarely "which seventh do I add" but "does this chord want a seventh at all". A plain triad has its own considerable virtue: it is clear, it is open, it gets out of the way of the melody. A great many of the best progressions are mostly plain triads with one seventh placed where it counts, the way a baker uses a pinch of salt and not a fistful. The restraint is not a smaller skill than the addition. It is the larger one.

How to feel the difference

You will learn this far faster with your ears than with your eyes, so let me send you to play rather than to read. Take a simple loop you already know, four plain triads going round, and add a single seventh to just one of them. The chord builder will let you do this in a few seconds: build the triad, hear it, then add the seventh and hear the same chord lean. Put the dominant seventh on the chord just before you return home, and listen to how much harder the song now pulls back to the start. Then take it off again and feel the room go quiet.

Once you can hear a seventh leaning, you will start noticing where the songs you love spend theirs, and you will notice they spend them sparingly. (If you want to keep going past the family chords, the borrowed chords primer is the next small detour worth taking.)

Add the note. Hear it lean. Then decide, every time, whether the chord was better leaning or better standing still.

...there.