Henry Watson Fowler, in The King's English, says "any definition of irony—though hundreds might be given, and very few of them would be accepted—must include this, that the surface meaning and the underlying meaning of what is said are not the same." Also, Eric Partridge, in Usage and Abusage, writes that "Irony consists in stating the contrary of what is meant."
The use of irony may require the concept of a double audience. Fowler's A Dictionary of Modern English Usage says:
Irony is a form of utterance that postulates a double audience, consisting of one party that hearing shall hear & shall not understand, & another party that, when more is meant than meets the ear, is aware both of that more & of the outsiders' incomprehension.[4]
The term is sometimes used as a synonym for incongruous and applied to "every trivial oddity" in situations where there is no double audience.[4] An example of such usage is:
Sullivan, whose real interest was, ironically, serious music, which he composed with varying degrees of success, achieved fame for his comic opera scores rather than for his more earnest efforts