ShadowSD said

[orig][quote]

-One common consequence of the fifth being more central identity than the third is the vii chord in major keys (or the the ii chord in minor keys) ending up NOT being diminished as it is in classical theory. For example, in the riff from I Don't Know by Ozzy in the key of Am (A B C D E F G), Rhoads plays a B power chord even though it has an F# instead of playing a B with a diminished fifth (F) just for the sake of staying in key, because it would actually be MORE dissonant to do so, despite conventional assumptions; in the second half of Fade To Black (in the key of Em), the same scenario occurs, as the F# is accompanied by it's fifth, a C#, instead of going with the diminished fifth (C) just to stay in key. Anyone who wants to get a feel for this principle, try playing those riffs the correct way and then the "in key" way, and watch the latter sound worse.