1. any demand that is critical or pressing. See categorical imperative; ethical imperative.

2. in psychoanalytic theory, a demand of the superego that represents the commanding voice of parental or social rule and operates on an unconscious level to direct the behavior of the individual.

3. in linguistics, the mood of a verb used to issue commands or make requests, as in Get off! or Please come back. Compare indicative; interrogative; subjunctive.