About the C#dim chord
To play C# diminished, use the first shape above. Place your index finger on the 1st fret of the C string and your pinky finger on the 4th fret of the A string. Leave the G and E strings open. Strum all four strings and check that each one rings cleanly.
Root
C#
Quality
Diminished
Notes
C# · E · G
How the C#dim chord works
Root(1)
The home note. It gives the chord its name.
Minor third(♭3)
The defining minor interval above the root.
Diminished fifth(♭5)
A lowered fifth that adds harmonic tension.
