Why are a diminished 7th and a major 6th (notes) called different names if they're both the same note? Which name would you use in certain situations?

This came up when I was explaining to my friend a diminshed 7th chord (1, b3, b5, bb7) and he said "Wait a minute. bb7? Isn't that the same as major 6th?" And I really couldn't give him an explanation to prove that they aren't the same.
Last edited by MeGaDeth2314 at Jul 24, 2006,
they are enharmonic equivalents, I think thats what its called, basically same note dif. name like you said, you could use whatever name you wanted, it doesn't really matter,diminished 7th is the more common name when you're talking about chords, note wise, major 6th is more common.
Quote by syyz1
You're right, I mean, I can imagine eating children, but listening to good music seems a little too much. You, Iruleeverything, are the master of torture.
Because in the notation you would have to sharp whatever the 6th was if it was a minor 6, and since you can only use all sharps or all flats in a piece of music, the only other option is to flat the 7 twice
that's like saying "why do they have a Gb and an F# when they're both the same note??" they're used in different context ... a Gb would be used in the context of an EbM chord or scale, while an F# would be used in the context of a D or G7 ... likewise if you're playing a diminished chord you use a double flat (bb) to demonstrate how you got to that chord theoretically ... in a Cdim7 for instance you use C, Eb, Gb, Bbb. since B is the 7th note in a C-scale it would be very confusing to say that C, Eb, Gb, A is a Cdim7 because it doesn't contain the 7th note of the scale at all, even though it does technically contain the right notes ... to use my original example, it's like writing the chord as C, D#, F#, A ... which doesn't look anything like a C chord ...
BM7 and D6 have same notes but are arranged differently so you get a somewhat different voicing.

Eagles "One Of These Nights" is a good example of this. Main part of song goes:

Em - BM7 - Cmaj7


Em - D6 - Cmaj7

I prefer the D6 version. Use what YOU think sounds best.
Well you could get an entirely different sound from those two chords, Bm7 and Dmaj6. If you replace one with the other in a given song, you could change all the dynamics of the movement of that section. You can't really just interchange them seamlessly. If the harmony dictates the root is B, then you play the Bm7... similarly for the Dmaj6.
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