Progressions in A — Cello

A major harmonises to A – Bm – C#m – D – E – F#m – G#°; A minor to Am – B° – C – Dm – Em – F – G. Each chord links to its tone map on the Cello, so a tune in A becomes a short list of places the hand needs to be.

The useful question in a key is which open strings it agrees with. In A, check the chords against the open C and A — a key that leaves an open string ringing under the melody is a key this instrument was built for.