(_a_) The current arguments for Subjectivism are often so stated as to confuse together two quite distinct positions. When it is said that what we perceive is “our own subjective states,” the meaning intended may be either that there is, at least so far as I am able to know, no real existence in the universe except that of my “states of consciousness”; or again, that there are such realities, but that the _properties_ which I perceive do not belong to them in their own nature but are only subjective effects of their action upon my “consciousness,” or, if you prefer to speak in physiological language upon my nervous system. Now, many of the arguments commonly urged by the subjectivist would at most only prove the second conclusion, in which the subjectivist agrees to a large extent with the scientific realist. Thus it is an _ignoratio elenchi_ to reason as if the facts of hallucination, illusion, and discrepancy between the reports of different percipients or different sense-organs of the same percipient gave any support to the special doctrine of Subjectivism. These facts, which, as we have seen, are equally appealed to by scientific realists, prove no more than that we do not always perceive the world of things as it is, and as it must be thought of if we would think truly,—in other words, that there is such a thing as error. Now the problem “How is it possible for us to think or perceive falsely?” is, as the student of Greek philosophy knows, both difficult and important. But the existence of error in no way shows that the things which I perceive are “states of my own consciousness”; on the contrary, error is harder to explain on the subjectivist theory than on any other. For if what I perceive has some kind of existence distinct from the mere fact of my perceiving it, there is at least a possibility of understanding how the reality and my perception of it may be discrepant; but if the existence of a thing is only another name for the fact that I perceive it, it seems impossible that I should perceive anything except as it is. On the subjectivist theory, as Plato showed in the _Theaetetus_, every percipient being ought, at every moment of his existence, to be infallible.