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I encountered the example in the picture above today, and I found it interesting because a secondary dominant had 2 tritones with addition of b9.

A tritone is an integral part to definition of the dominant seventh chord. Doesn't having two tritones sabotage its definition?

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  • Why do you think it would “sabotage the definition”? How could a b9 not add an extra tritone?
    – PLL
    Commented Jun 12 at 8:23
  • @PLL actually a good question: if we omit the fifth, which is often done, there will be no second tritone. Commented Jun 12 at 14:54
  • @user1079505 "If my grandmother had wheels" :)
    – sehe
    Commented Jun 12 at 19:38

2 Answers 2

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Yes, a dominant chord with b9 has two symmetrically displaced tritones. It it creates an ambiguity which can be used creatively, as you can resolve the chord in 4 different ways: to E (or Em, your example), but also to Bb (this is called "tritone substitution"), and less commonly to G or to Db.

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It's the tritone F♯ and C♮ that is operational mainly - leading to the G and the B of, in this case, E minor.

Adding the other two notes produces a fully diminished chord (all notes are m3 apart), and as we know, that will make another tritone. Diminished chords are useful to change from one chord to an unexpected one (if needed), so yes, all is well. The bassline does its 'proper' job of secondary dominant, moving from B>E.

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