Even if they are, psychologically considered, identical operations, perception and memory are in general sufficiently marked off by a speciality in the form of the operation.

Thus, while memory is the reproduction of something with a special reference of consciousness to its past existence, perception is the reproduction of something with a special reference to its present existence as a part of the presented object.

In other words, though largely _representative_ when viewed as to its origin, perception is _presentative_ in relation to the object which is supposed to be immediately present to the mind at the moment.[3] Hence the convenience of recognizing the popular classification, and of making it our starting-point in the present case.
All knowledge which has any appearance of being directly reached, immediate, or self-evident, that is to say, of not being inferred from other knowledge, may be divided into four principal varieties: Internal Perception or Introspection of the mind's own feelings; External Perception; Memory; and Belief, in so far as it simulates the form of direct knowledge.

The first is illustrated in a man's consciousness of a present feeling of pain or pleasure.

The second and the third kinds have already been spoken of, and are too familiar to require illustration.