F# Diminished (F#dim)
Also written as Gb Diminished (Gb and F# are the same key).
1+b3+b5
Notes in F# Diminished
F# (root)AC
Inversions
Same notes as F# Diminished, with a different chord tone as the lowest note. Useful for smoother movement between chords instead of jumping around the keyboard.
Root position
F# in the bass
1st inversion
A in the bass
2nd inversion
C in the bass
Play F#, A and C together and you get F# Diminished.
Stack two minor thirds and the fifth shrinks along with the third, producing a triad that never feels at rest. Diminished chords are unstable by design, built to lean somewhere else, usually resolving up by a half step. Played alone it can sound almost comical, but tucked between two other chords it's one of the most useful tension devices in tonal music.