  Riddles based on simple puns can be classified according to the patterns of
word, syllable or phrase similarity they depend upon. We have devised a formal
model of the semantic and syntactic regularities underlying some of the simpler
types of punning riddle. We have also implemented this preliminary theory in a
computer program which can generate riddles from a lexicon containing general
data about words and phrases; that is, the lexicon content is not customised to
produce jokes. Informal evaluation of the program's results by a set of human
judges suggest that the riddles produced by this program are of comparable
quality to those in general circulation among school children.
