How to play C7 (C 7) on Guitar

C7 is the C 7 chord. It is built from 4 notes — C, E, G and A# — which sit at the root, major third, perfect fifth and minor seventh above the root C. Written as a formula that is 1P – 3M – 5P – 7m. Those intervals, not the note names, are what give the chord its character: move all of them to a different root and you still hear a 7 chord.

C7 on guitar is an open shape — 1 string rings open while 4 are fretted, the shape spans 3 frets, 1 string is muted and should not sound — damp it with the underside of a fretting finger. Open strings do a lot of the work here, which is why this shape sounds fuller than the effort it takes. Arch your fingers so each one lands on its fingertip — a finger leaning flat will deaden the open string next to it, and a single muted string is the most common reason a beginner's chord sounds wrong when the fingering is in fact correct.

The major third between C and E is what makes this chord sound bright and settled. Flatten that one note by a semitone and you have C minor instead — a single semitone is the whole distance between the two moods. The added minor seventh stops the chord from sounding like a resting place — it leans forward and wants to resolve, which is exactly why it turns up at the end of a phrase rather than the start.

C7 belongs to 1 major key, including F major, where it is the V chord. That is the practical reason to learn it: a chord that is diatonic to several keys turns up constantly, and knowing which degree it occupies tells you what tends to come next. A V chord in F major most often moves toward the tonic, so practising C7 in the context of F will teach you more than practising it in isolation.