Brewer's Dictionary of Phrase and Fable explains solecism as follows:
Misapplication of words; an expression opposed to the laws of syntax; so called from the city of Soli, in Cilicia, where an Athenian colony settled, and forgot the purity of their native language.
In prescriptive linguistics, a solecism is a grammatical mistake or absurdity. Here are some examples of usages often regarded as solecisms in standard English:
- "This is just between you and I" for "This is just between you and me." (hypercorrection to avoid the common, non-standard "you and me" form in the subject of sentences while "me" is, nonetheless, the standard pronoun for the object of a preposition.)
- "He ain't going nowhere" for "He isn't [or he's not] going anywhere." (dialectic usage; see "ain't")
- "Whom ate the food?" for "Who ate the food?" (hypercorrection resulting from the perception that "whom" is a formal version of "who")
- "He's the person whom I believe is the fastest" for "He's the person who I believe is the fastest." (hypercorrection resulting from the perception that the relative pronoun is functioning as an object in the dependent clause when, in fact, it is a subject, with the predicate "is the fastest"; contrast "whom I believe to be the fastest," in which "whom" is the object of "I believe")
- "Irregardless" for Regardless (nonstandard neologism from analogy with constructions like "irreverent" and "irrevocable," where the negative prefix in- changes to ir-).
What is considered a solecism in one register of a language may be acceptable usage in another. For example, "The world keeps turning for you and I" (10cc) is acceptable as a song lyric (see poetic license) but is considered a solecism in standard English. Rejecting convention in favor of consensus, modern descriptive linguistics generally dismisses the notion of solecisms, concentrating on how language is used, rather than how it ought to be used.
Note that a solecism is an error of syntax, while a barbarism is an error of morphology.