canon at the octave in which the vv. (human or instr.) are at that pitch‐interval from one another. canon at the fifth, or at any other interval, is similarly explained.
A canon for 2 vv. is called a canon 2 in 1 (and similarly with canon 3 in 1, etc.). A canon 4 in 2 is a double canon, i.e. one in which 2 vv. are carrying on one canon whilst 2 others are engaged on another.
canon by augmentation has the imitating vv. in longer notes than the one that they are imitating. canon by diminution is the reverse. canon cancrizans is a type in which the imitating v. gives out the melody backwards (‘cancrizans’ from Lat. cancer = crab; but crabs move sideways). Other names for it are canon per recte et retro (or rectus et inversus) and retrograde canon.
A perpetual canon or infinite canon is a canon so arranged that each v., having arrived at the end, can begin again, and so indefinitely as in Three blind mice. The converse is finite canon.
strict canon in which the intervals of the imitating v. are exactly the same as those of the v. imitated (i.e. as regards their quality of major, minor, etc.).
In free canon the intervals remain the same numerically, but not necessarily as to quality (e.g. a major 3rd may become a minor 3rd).
That v. in a canon which first enters with the melody to be imitated is called dux (leader) or antecedent, and any imitating v. is called comes (companion) or consequent.
In canon by inversion (also styled al rovescio), an upward interval in the dux becomes a downward one in the comes, and vice versa. canon per arsin et thesin has the same meaning, but also another one, i.e. canon in which notes that fall on strong beats in the dux fall on weak beats in the comes, and vice versa.
Choral canon in which there are non‐canonic instrumental parts is accompanied canon.
Passages of canonic writing often occur in comps. that, as wholes, are not canons. In addition to actual canonic comp. there exists a great deal of comp. with a similar effect but which is too free to come under that designation, being mere canonic imitation.