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Would anybody know the parent major scale of F sharp minor 7 flat 5?

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G major. F#, A, C, E make F#m7b5, the 4 note chord based on the leading note of G major. The triad would be F#o, and your chord is sometimes called F# half-diminished. There's a sign, but I can't find it!

  • The diminished chord is a superscripted little circle like you approximated with an 'o'. The half-diminished chord is the same but with line through it like this ø. Is that what you meant? Or you just couldn't find how to type the character? Either way... – user37496 Apr 26 '17 at 12:52
  • I haven't got to where I am without knowing..! The approximation is actually dim - F#o. But I don't know how to make half-dim with a qwerty board. – Tim Apr 26 '17 at 14:06
  • Press/hold the "alt" key and type 232 on the 10-key num pad to get this symbol: Φ Hope this helps! – Random dude Sep 13 '17 at 22:19
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    ø - It's here: en.wikipedia.org/wiki/Half-diminished_seventh_chord You can just cut and paste it from here or any place you find it on interweb - put one aside if you like. – Stinkfoot Sep 14 '17 at 3:43
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    @Greg - yes, either will work, 'cos every other note from them is contained within the chord - assuming you pick the right one from three! However, m7b5 is not a dim chord - it's only sort of half dim. The m7 bit is what makes the difference: dims have a dim7, a semitone lower than the b7 (m7). – Tim Sep 14 '17 at 14:37
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There are two likely choices for the parent scale of an F♯-7(♭5) chord, also known as an F♯∅ or half-diminished chord.

This chord can be built on the seventh degree (or the Locrian mode) of the major scale, meaning that G major could be thought of as the parent scale for this chord. From F♯ Locrian this gives:

    F♯  A   C   E   G   B   D  
    1  ♭3  ♭5  ♭7  ♭9   11 ♭13

But you can also build this chord on the sixth degree (or the Locrian #2 mode, or the half-diminished mode) of the melodic minor scale. This would make the A melodic minor scale a parent scale of the half-diminished chord. From F♯ Locrian #2 this gives:

    F♯  A   C   E   G♯  B   D  
    1  ♭3  ♭5  ♭7   9   11 ♭13

Note that the only difference between these two approaches is in the 9th. The Locrian mode from the major scale provides a lowered 9th; this is sometimes called an "avoid" note since it is a half-step above a chord tone and is harmonically unstable. The Locrian #2 mode from the melodic minor scale provides a natural 9th. None of the upper extensions are a half-step above a chord tone, so there are no "avoid" notes here.

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One cannot find the parent scale from just a chord. Maybe it could be a G major, but this chord could be also a Dominant of Dominant (D.D) VII7, which leads to G major, which is the V of C scale

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    Given a major triad, there would be three diatonic possibilities: e.g. (D F# A) is in the keys of G, D, and A. The same could be said for minor triads. But a m7b5 chord narrows down the diatonic possibilities to one. – The Chaz 2.0 Jan 25 '18 at 20:09

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