Diminished 7th Chord
Jen P., Utah
I was helping a student with a chord in her accompaniment project today that was F#dim7. The way we figured it out it looks like an FM7. Is there a reason it would be written specifically as a dim chord? The previous chord was F so it didn’t make sense that it was keeping with an F# pattern or anything.
Mark M., New York
F#dim7 is F#, A, C, Eb. This is because a dim7 chord is a diminished chord plus a double-flatted 7th. If you wanted a SM-like Acc1-like way of playing it, you’d take the major triad and turn it into a diminished in the standard way by flatting the 3 and 5 (A and C) and then you’d reach the thumb down to the Eb.
The “triangle” diagram would have the 1 down 1.5 steps while the 3 and 5 are each down the usual half step for diminished chords.
There is more than one kind of 7. A maj7 chord adds a major 7th interval, which is not flatted at all. A dim7 chord adds a diminished 7, which is double flatted. In between, the single-flatted 7 is used for dominant 7 chords, and for minor 7 chords, and also for what is called a half-diminished 7 or even just a half-diminished chord. This latter is what you had in mind.
Maureen K., California
I do find it helpful to notice that it is the same as an F7 (not an FM7 as you thought), except the F note is replaced by F#. I find that those diminished chords are often transition chords.
Mark M., New York
Yup! This is why, in the Music for Christmas and the New Year supplemental accompaniment program, Neil teaches moving from, e.g., D to D#dim as simply raising the thumb, a nice playing-based way of doing it without having to yet teach/inherit diminished chords in general.
Joanne D., Australia
I love that diminished 7ths are just a set of minor 3rds and I find that the easiest way to remember them
Original discussion started July 15, 2019