Seventh Chords — What Adding One Note Changes

Add a fourth note to a triad and a colour becomes a sentence

Add one more note to a triad and it sounds completely different. The point of this page: the added note is not decoration — it changes the chord's function.

The three sevenths you hear most

One: major seventh (C E G B) — bright, with a touch of suspension.

Two: dominant seventh (C E G B♭) — the one of the three that most wants to go somewhere.

Three: minor seventh (C E♭ G B♭) — dark, but steadier than a bare minor triad.

The key: the added note changes *what*

A triad is a static colour. Once a seventh is added, it becomes an unfinished sentence:

• the minor seventh of the dominant chord (B♭ over C) must fall a semitone to reach the tonic (C → B);
• the major seventh also falls, but lands somewhere different;
• the minor seventh of the minor seventh chord (B♭) likewise has to fall.

So the right way to hear a seventh chord is not "what colour is it" but "where does the lower note want to go". That is the same logic as the diminished triad — an unstable interval is itself a direction.

An action you can verify yourself

1. Listen only to the first (major seventh) as a block; 2. Then only to the second (dominant seventh) as a block; 3. Alternate between them quickly — you will notice major seventh and dominant seventh sound like completely different things, though they differ by one note (B versus B♭).

That is what half a semitone is worth. It turns a stable chord into one that wants to resolve.

What sevenths actually do in music

The job of a seventh is not "more richness" — it is "to give it direction":

• dominant → tonic: the engine of every cadence;
• major seventh: makes the tonic feel unfinished, or lyrical;
• minor seventh: gives a dark chord a dignified ending.

So if you are writing an ending, the seventh before the final chord often decides whether it works better than the final chord itself.

Next

• The triad foundation: three chord qualities
• Does position change the sound?: inversions
• The second before it resolves: suspensions
• Sevenths in combination: the three commonest progressions

Sources

• 本页为七和弦对比练习的说明；和弦构成依据通用乐理记法
• 实例均标注来源与许可档位，可在线试听；练习用的合成音由浏览器实时生成，非录音

Used for fact-checking only; all prose is original.