Acting has been variously defined as impersonating, imitating, interpreting, creating, feeling, radiating, being, behaving, or believing. Acting has even been defined as acting. In his book, The Actor's Ways and Means, Michael Redgrave states:
The essence of acting… is the power to act. Thought or emotion may or may not be present—but the basic will of the actor must be, quite simply, to act: not to think, not to feel, not to exhibitionize, not to make some personal statement—though he may do one or all of these—but to act.
Established actors, needing no definition, may accept any misty generalization if they are not sure what it is they are doing. The student actor needs a definition to guide him in understanding the process at any specific moment in the performance. The least common denominator in the actor's performance is a single unit. This unit is compounded of a stimulus and a response.