Chord Formulas

[JonPR]

Originally Posted by Big Band Guitar

Not to be picky, but I'm going to be.

Diminished chord is a triad.
Diminished 7 is a 4 note chord.

I use them interchangeably.

Well, I can be picky too!
They're not always interchangeable. I.e., a dim triad can always be played instead of a dim7 (any triad out of te 4 notes), but vice versa doesn't always apply. Sometimes a dim triad needs a minor 7th, not a dim7. A ii chord in a minor key, for example is a half-dim (m7b5), not a dim7.
vii in a major key is more debatable. Sometimes the diatonic viim7b5 (rootless V9) is right, sometimes the chromatic viidim7 (from parallel harmonic minor) is better.

[Big Band Guitar]

Originally Posted by JonPR

Well, I can be picky too!
They're not always interchangeable. I.e., a dim triad can always be played instead of a dim7 (any triad out of te 4 notes), but vice versa doesn't always apply. Sometimes a dim triad needs a minor 7th, not a dim7. A ii chord in a minor key, for example is a half-dim (m7b5), not a dim7.
vii in a major key is more debatable. Sometimes the diatonic viim7b5 (rootless V9) is right, sometimes the chromatic viidim7 (from parallel harmonic minor) is better.

I stated nothing about m7b5 that is a very different subject.

I did NOT say dim and dim7 were interchangeable I said I use the dim and the dim7 interchangeably.