Perception has already been partially defined. So-called 'external objects' are forms excited in our consciousness by pressure of other minds. The great permanent 'world' is due to the action of a cosmic mind with which we are intimately associated throughout our physical life.

Objects have a totally different sort of existence from minds, for whereas the latter are—at least relative to objects—self-existent, the former have no existence except during the act of perception. If minds could be all moved asunder from each other the whole objective world would disappear, yet the universe would be as full as before, for sensation occupies no room.

The appearances we interpret as distance are due to variations in the pressure or stimulus producing the object.

It will be convenient to call the more active mind Noumenon, the perceiving mind Subject. The mind that is subject on one occasion may be noumenon at another, and conversely. The true antithesis to subject is not object, but noumenon. Object has no antithesis, unless it be nonentity.

It is specially to be noticed that an object is not the cause of a sentiment. The knife we see or handle is not the cause of the pain it may inflict if driven into our flesh. Pains and pleasures signify that the noumenal action is powerful enough not only to excite objects in the intellect, but to penetrate inwards and excite sentiments also. It is the noumenon that causes both object and sentiment, as far as the energy exerted is concerned, but the variation of plasma in the subject is also essential to the distinction of object and sentiment.

The subject is not quite passive in perception. No consciousness takes place unless the subject is charged with energy. Further, since consciousness is confined to the Self and not inherent in the plasma, we perceive only such vibrations as reach the Self. If the Self is absorbed in one part of the mind, vibrations may take place in other parts without being noticed. The more energy we concentrate at the point or surface of contact (Attention), or otherwise bring to bear on the plasmic vibration, the more vivid is the object.

The fixing or circumscribing of attention so as to break up our experience into distinct things or objects is an acquired art, whence we may infer that the intellectual experience of infancy is a vague whitish surface, not clearly distinguished by colour or movement.

Kant and other philosophers admit that objects are caused by noumena, but insist that we can never know or conceive what a noumenon is.

Why not? Each of us knows himself to be the noumenon of many phenomena; he has no doubt that many other phenomena are caused by minds like himself, and it is easy to extend this principle to all phenomena whatever. They are all caused by minds more or less like human minds. This is a useful conclusion, although we are not able to imagine very accurately the mind of an insect or of a being of cosmic dimensions. It is not necessary we should, but the most general inference of this sort is better than none at all, and better than the notion that phenomena are self-existent and self-moving.

Although simple and intelligible when stated in the abstract, perception is difficult to work out in detail. Objections start up on every side, and it requires the utmost patience to reduce them to what they are—inferences from the realism we are supposed to have discarded. It is only when we try to dislodge realism wholly and consistently that we find how fast its hold upon our intellect is. Critics who profess to treat Berkeley's substantialism seriously and sympathetically, constantly bring up against it arguments of the most naively realistic kind. They have no adequate conception how enormous is the revolution in thought involved in substituting substantialism for realism. It is a complete dissolution of the natural thought and belief; it means the construction of a new heaven and a new earth with laws to which we have been hitherto unaccustomed. The old science is of little or no use to us as substantialists.

Philosophy is not an advance or correction of science. In so far as the latter claims to be absolutely or philosophically true, substantialism abolishes it in dispensing with the notions of real matter and real space. Hence it is quite irrelevant to point out that substantialism is inconsistent with (say) the doctrine of physical evolution. This theory, though so new, is now often referred to as axiomatically true, whereas it is an inference, the evidence for which, even to many realists, is far from conclusive. Whether it be considered true or not in science, physical evolution is quite untrue in philosophy.