| Definition -
A sentence in which a noun or noun phrase is identified with another noun or noun phrase, e.g. Harper is the Prime Minister.
As opposed to an ascriptive sentence in which some property is ascribed to the subject, e.g. Bob is a fool.
1. Equational sentences differ from ascriptive sentences because they can be inverted without losing their sense, e.g. The Prime Minister is Harper, but not A fool is Bob.