qualities of things are all resolved into general and special phenomena,
appearances, and extrinsic forms, as far as animal and human intuition,
and the character of the subject which perceives and feels them, are
concerned; and they are perceived just so far as we and as animals are
able to communicate by means of our senses with the world and with
ourselves. A phenomenon and an intrinsic form signify, at the moment of
perception, the thing, the object which the conditions of our senses
enable us to perceive, and the intrinsic power of this phenomenon
implies a cause. Natural phenomena and beings are thus reciprocally
linked together as causes and effects, an effect becoming in its turn
the cause of a subsequent fact; that is, when we consider things in
themselves, and not relatively to the animal or man who apprehends them.

If, therefore, there are in animal consciousness and intelligence three
elements of apprehension, afterwards fused into a single fact, it
follows that the extrinsic relations of beings and forces are
subjectively reciprocal; there is the given form of a phenomenon, and,
intrinsically, it consists of an active power, eternally at work, since
there is no being nor form which stands still and is not reproduced in
the infinite evolution of the universe.

Since, to the percipient, the extrinsic form, whatever it may be,
remains the same as that which was first presented to him, the
phenomenon is bounded by his faculty of perception, followed by the
immediate and implicit assumption of a subject, and consequently of a
possible and indefinite causality. This internal and psychical process
of the animal corresponds with the actual condition of things, as they
appear and really are; a correspondence which is in itself a powerful
confirmation of the truth.