The building-block of man’s knowledge is the concept of an “existent” — of something that exists, be it a thing, an attribute or an action. Since it is a concept, man cannot grasp it explicitly until he has reached the conceptual stage. But it is implicit in every percept (to perceive a thing is to perceive that it exists) and man grasps it implicitly on the perceptual level — i.e., he grasps the constituents of the concept “existent,” the data which are later to be integrated by that concept. It is this implicit knowledge that permits his consciousness to develop further.
(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.)
The (implicit) concept “existent” undergoes three stages of development in man’s mind. The first stage is a child’s awareness of objects, of things — which represents the (implicit) concept “entity.” The second and closely allied stage is the awareness of specific, particular things which he can recognize and distinguish from the rest of his perceptual field — which represents the (implicit) concept “identity.”
The third stage consists of grasping relationships among these entities by grasping the similarities and differences of their identities. This requires the transformation of the (implicit) concept “entity” into the (implicit) concept “unit.”