Diminished and Half-diminished 7th Chords

Diminished Seventh Chord	Theory Things William Wieland
3 3 3 (½ steps), i.e. all minor 3rds (Keyboard) diminished triad + diminished 7^th (2 minor 3rds + an augmented 2nd smaller than an octave) Lower 3, 5, & 7 of a V⁷. (G - B - D - F becomes G - B flat - D flat - F flat.) In minor, build a seventh chord on the leading tone: ti - re - fa - le. (a minor: g sharp - b - d - f)
Half-diminished Seventh Chord
3 3 4 (½ steps) (Keyboard) diminished triad + minor 7^th (2 minor 3rds + a major 2nd smaller than an octave) (The minor 7^th is also used in the V⁷.) Lower 3 & 5 of a V⁷. (G - B - D - F becomes G - B flat - D flat - F.) In major, build a seventh chord on the leading tone: ti - re - fa - la. (C major: B - D - F - A)
Diminished and Half-diminished Seventh Chord Quiz
Diminished Seventh Chords at the Piano