  This article proposes a cognitive mechanism of humour of general
applicability, not restricted to verbal communication. It is indebted to
Raskin's concept of script overlap, and conforms to the incongruity-resolution
theoretical framework, but it is built on the notion of constraint, an abstract
correspondence between sets of data. Under this view, script overlap is an
outcome of a more abstractly described phenomenon, constraint overlap. The
important concept of the overlooked argument is introduced to characterise the
two overlapping constraints -- overt and covert. Their inputs and outputs are
not directly encoded in utterances, but implicated by them, and their overlap
results in another overlap at the level of the communicated utterances, that
the incongruity reveals. Our hypothesis assumes as a given that the evocation
of such constraints is a cognitive effect of the inferential process by which a
hearer interprets utterances. We base this assumption on Hofstadter's theory of
analogy-making as the essence of human thought. By substituting "stimuli" of
any kind for "utterances" in this model, we obtain a mechanism as easily
applicable to non-verbal communication -- slapstick, cartoons -- and we propose
it describes the necessary and sufficient conditions for a communicative act in
any modality to carry humour.
