The standard dictionary definition of a metaphor--a word or phrase applied to an object or concept that it does not literally denote in order to suggest comparison with another object or concept--is inadequate in that it does not deal with whole sentence metaphors and that it provides no way of distinguishing between a metaphor and a semantic anomaly or a falsehood. A superior, alternative definition is that a metaphor is the use of an expression that is contextually anomalous and for which the metaphoric tension is in principle eliminable. Tension elimination can be conveniently discussed in terms of three functions that metaphors can perform: expressing things that are literally inexpressible, conveying concepts in a compact manner, and expressing ideas vividly. Results of experiments on the comprehension of metaphors suggest that two important variables affecting the comprehension of nonliteral uses of language in general, and of metaphors in particular, are the nature of and the amount of contextual support. Finally, it might seem that there is an important difference between metaphors and similes because the apparent violation of conversational postulates, at least of the sincerity postulate, is immediately obvious in the case of the metaphor, but much less obvious for the simile. (GW)