But assuming western European music, which is the idiom in which Bach wrote, 24 keys are all there are. 12 major keys and their relative minors, which makes a total of 24. One prelude in each, one fugue in each.

24 x 2 = 48.

Unless they've changed the laws of mathematics—no, simple arithmetic—I count a total of 48 individual pieces althogether.

Don Firth

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