Although, chronologically, man’s consciousness develops in three stages: the stage of sensations, the perceptual, the conceptual — epistemologically, the base of all of man’s knowledge is the perceptual stage.
Sensations, as such, are not retained in man’s memory, nor is man able to experience a pure isolated sensation. As far as can be ascertained, an infant’s sensory experience is an undifferentiated chaos. Discriminated awareness begins on the level of percepts . . .
Percepts, not sensations, are the given, the self-evident. The knowledge of sensations as components of percepts is not direct, it is acquired by man much later: it is a scientific, conceptual discovery . . . .
(It may be supposed that the concept “existent” is implicit even on the level of sensations — if and to the extent that a consciousness is able to discriminate on that level. A sensation is a sensation of something, as distinguished from the nothing of the preceding and succeeding moments. A sensation does not tell man what exists, but only that it exists.)