Kenneth G. Wilson (1923–). The Columbia Guide to Standard American English. 1993.
its, it’s
The genitive of the pronoun it is its, without an apostrophe; the contraction of it is is spelled it’s, with an apostrophe. Most errors involve using the contraction when the genitive is intended; these are usually the errors of inattention or carelessness, but they’re often judged as though ignorance caused them, so inspect carefully what you write.
