“1. The words in a text, usually a noun phrase, to which a pronoun or other grammatical unit refers back. Cook is the antecedent of him in: ‘In 1772. Cook began his second voyage, which took him further south than he had ever been.’ Similarly, his second voyage is the antecedent of which. With impersonal it, this, that, which, the antecedent may be a whole clause or paragraph, as in: ‘Might not the coast of New South Wales provide and armed haven? To some people this looked good on paper, but there is no hard evidence that it did so to William Pitt or his ministers.’ Despite the implications of the name, an antecedent can follow rather than precede: ‘For his first Pacific voyage, Cook had no chronometer.’ 2. In logic, the conditional element in a proposition. In If they did that, they deserve our respect, the antecedent is they did that.”
Excerpted from: McArthur, Tom. The Oxford Concise Companion to the English Language. New York: Oxford University Press, 2005.