  Fine's influential Canonicity Theorem states that if a modal logic is
determined by a first-order definable class of Kripke frames, then it is valid
in its canonical frames. This article reviews the background and context of
this result, and the history of its impact on further research. It then
develops a new characterisation of when a logic is canonically valid, providing
a precise point of distinction with the property of first-order completeness.
The ultimate point is that the construction of the canonical frame of a modal
algebra does not commute with the ultrapower construction.
