Chord Types

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What is a chord?

At its simplest, a basic Chord (a Triad) has 3 different notes, each of which may be repeated in different octaves.
To name the chord, we juggle the notes into “Root Position”, so that the 3 notes are 2 notes apart (eg C E G)

A Major Chord in Root position has 3 notes each with a gap between them (eg C E G)
The notes are spaced with 4 semitones (4 frets) between the first two, 3 between the next
The gap between the top and bottom is 7 and is a “perfect fifth”
If the starting note is placed on top as well (eg C E G C) the gaps are 4 3 5

A Minor Chord in Root position has 3 notes with the same one-letter gap (eg A C E)
The notes are spaced with 3 semitones between the first two, 4 between the next
The gap between the top and bottom is again 7 and is a “perfect fifth”
If the starting note is placed on top as well (eg A C E A) the gaps are 3 4 5

An Augmented Chord has 3 notes with the same one-letter gap (eg G D B#)
The notes are spaced with 4 semitones between the first two, and 4 between the next
The gap between the top and bottom is 8 and is an “augmented fifth”
If the starting note is placed on top as well (eg G B D# G) the gaps are 4 4 4
A correctly written augmented chord always has an accidental somewhere

A Diminished Chord has 3 or 4 notes with the same one-letter gap (eg B D F or B D F Ab)
The letter names are spaced with 3 semitones throughout
The gap between the first three notes is 6 and is an “diminished fifth”
If the starting note is placed on top as well (eg B D F Ab B) the gaps are 3 3 3 3
A correctly written diminished chord always has an accidental somewhere

A Half Diminished Chord has four letter names with the same one-letter gap (eg B D F A)
The letter names are spaced 3, 3, 4, 2 semitones apart
The gap between the first three notes is 6 and is an “diminished fifth”
If the starting note is placed on top as well (eg B D F A B) the gaps are 3 3 4 2
A correctly written half diminished chord may not always have notes outside of the key signature
It’s worth noting that this half-diminished chord is sometimes called Bm7b5.
More confusingly, if the bottom note is D, then the same notes form Dm6, which isn’t diminished at all!

Any numbers after the chord denote the addition of an extra note at that interval. For example G7 includes an F because G-F is an interval of a seventh.
We don’t discuss here the circumstances in which a chord can be reduced to 2 letter names and still function.