Originally posted by griphon2
[B]Your explanation of tonic, supertonic, mediant, I'll accept. As far as I'm concerned, 40 years writing, it's useless information. Nice questions on a test.

Yeah. But it can have it's uses when it comes to understanding what the chord names mean. Especially the "leading tone" which has a little theory behind it that still is very beneficial to understand.

As for tritones, I don't think you're gettin' it. The tritone is the Maj 3rd and the b7th of a dominant chord.
The interval is a tritone. Or a #4 or b5 or the devil's interval. A fully diminished chord is a double tritone. e.g., D7 and Ab7, both chords' tritone are exactly the same.(diminished can be used and thought of as dominant or leading tone, therefore, a function of the dominant, or pentultimate to I or i or other variations)

I get it, and I don't necessarily disagree but I don't think of a tri-tone as always being a dominant chord. We have two different views on the matter. When we were talking about chordal names in a key signature, I'm saying that the tri-tone exists within the IV chord from it's root to the 4th. I know your talking about the dominant 7 chord now. The part that I see different is the fact that every time you have a tri-tone the chord can or worse has to be looked at as a dominant. A tri-tone can exist in a minor 6th chord from the 3rd to the 6th, and is often the tonic chord in the melodic minor key. A completely separate function from what your saying, and it’s an apposite cadence when coming from a V7.

Although a diminished chord can be looked at as a dominant (if you wish), they have 2 different functions. A dominant chord resolving back to I has the effect of being a perfect cadence. On the other hand a diminished doesn’t and it is imperfect. A Dominant chord can resolve to the vi chord (V7-vi), a cool little trick cause your expecting it to resolve to I instead you get a different movement, but just as fulfilling. Referred to as a deceptive cadence. However a diminished chord hardly ever resolves to a vi, or simply up a whole step.