How to play C7 (C 7) on Bass

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 bass is a movable shape with no open strings, fretted between fret 8 and fret 10, the shape spans 3 frets, 2 strings are muted and should not sound — damp them with the underside of a fretting finger. Since the shape uses no open strings it is fully movable: slide it one fret higher and you have the same chord a semitone up, which is the cheapest way to learn eleven more chords from one hand position.

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.