On the other hand, we must all admit that when the plain man is not thinking about the distinction between ideas and things, but is looking at some material object before him, is touching it with his fingers and turning it about to get a good look at it, it never occurs to him that he is not directly conscious of the thing itself.

He seems to himself to perceive the thing immediately; to perceive it as it is and where it is; to perceive it as a really extended thing, out there in space before his body.  He does not think of himself as occupied with mere images, representations of the object.  He may be willing to admit that his mind is in his head, but he cannot think that what he sees is in his head.  Is not the object there? does he not see and feel it?  Why doubt such evidence as this?  He who tells him that the external world does not exist seems to be denying what is immediately given in his experience.

The man who looks at things in this way assumes, of course, that the external object is known directly, and is not a something merely inferred to exist from the presence of a representative image.  May one embrace this belief and abandon the other one?  If we elect to do this, we appear to be in difficulties at once.  All the considerations which made us distinguish so carefully between our ideas of things and the things themselves crowd in upon us.  Can it be that we know things independently of the avenues of the senses?  Would a man with different senses know things just as we do?  How can any man suffer from an hallucination, if things are not inferred from images, but are known independently?

The difficulties encountered appear sufficiently serious even if we keep to that knowledge of things which seems to be given in common experience.  But even the plain man has heard of atoms and molecules; and if he accepts the extension of knowledge offered him by the man of science, he must admit that, whatever this apparently immediately perceived external thing may be, it cannot be the external thing that science assures him is out there in space beyond his body, and which must be a very different sort of thing from the thing he seems to perceive.  The thing he perceives must, then, be appearance; and where can that appearance be if not in his own mind?

The man who has made no study of philosophy at all does not usually think these things out; but surely there are interrogation marks written up all over his experience, and he misses them only because he does not see clearly.  By judiciously asking questions one may often lead him either to affirm or to deny that he has an immediate knowledge of the external world, pretty much as one pleases.  If he affirms it, his position does not seem to be a wholly satisfactory one, as we have seen; and if he denies it, he makes the existence of the external world wholly a matter of inference from the presence of ideas in the mind, and he must stand ready to justify this inference.