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.
IDEAS
VIII—HOW PRODUCED
An imprint or mould of the object is generally left in the plasma of the subject. The imprint is deep, clear and lasting in proportion to the strength of the exciting cause and the degree of energy assigned to the perception. When the noumenon withdraws the object does not at once disappear, for if the energy of attention remain the mould left by the noumenon serves to excite a consciousness similar to the object, and this is what we call an Idea.
What Hume says as to an object differing from an idea in nothing but vividness is evidently incorrect. Objects are generally, but not always, more vivid than ideas, and when an object is present we have an indefeasible conviction of being acted on by something not ourselves, which conviction is not present in recollection. We may not be able to give a satisfactory reason for the conviction—if we are arguing idealistically we certainly shall not—but the fact that it is there serves to mark off objects as a class of consciousness distinct from ideas, irrespective of their vividness. If an object were once seen clearly and so remembered, and were afterwards seen indistinctly through a mist, the latter consciousness would (according to Hume) be the idea and the former the object. Such an application of words would be an abuse of language.
There are of course no innate ideas of objects. There is innate consciousness—the sentimental.