When I was an undergraduate attempting to write canons, it would have been convenient to have known that composers cheated. By the time I was a don, in turn trying to teach undergraduates to write canons, I now had this knowledge, though I would doubtless have called it ‘composers' expertise’; but, unfortunately, I was still not aware of the precise way in which this expertise was employed. Later, I found out that many canons (such as those of Bach's ‘Goldberg Variations’) were written on the scaffolding of a ground bass; although Bach's use of this bass is here obvious, as it is in Pachelbel's more mundane canon on the same ground, composers would often cover their tracks by removing the scaffolding from the finished work.