We have seen above that the world of real things in which the plain man finds himself is a world of objects revealed in experiences of touch.  When he asks regarding anything:  How far away is it?  How big is it?  In what direction is it? it is always the touch thing that interests him.  What is given to the other senses is only a sign of this.

We have also seen (section 8) that the world of atoms and molecules of which the man of science tells us is nothing more than a further development of the world of the plain man.  The real things with which science concerns itself are, after all, only minute touch things, conceived just as are the things with which the plain man is familiar.  They exist in space and move about in space, as the things about us are perceived to exist in space and move about in space.  They have size and position, and are separated by distances.  We do not perceive them, it is true; but we conceive them after the analogy of the things that we do perceive, and it is not inconceivable that, if our senses were vastly more acute, we might perceive them directly.

Now, when we conclude that the things directly perceptible to the sense of touch are to be regarded as appearances, as signs of the presence of these minuter things, do we draw such a conclusion arbitrarily?  By no means.  The distinction between appearance and reality is drawn here just as it is drawn in the world of our common everyday experiences.  The great majority of the touch things about us we are not actually touching at any given moment.  We only see the things, i.e. we have certain signs of their presence.  None the less we believe that the things exist all the time.  And in the same way the man of science does not doubt the existence of the real things of which he speaks; he perceives their signs.  That certain experiences are to be taken as signs of such realities he has established by innumerable observations and careful deductions from those observations.  To see the full force of his reasonings one must read some work setting forth the history of the atomic theory.

If, then, we ask the question:  What is the real external world? it is clear that we cannot answer it satisfactorily without taking into consideration the somewhat shifting senses of the word “real.”  What is the real external world to the plain man?  It is the world of touch things, of objects upon which he can lay his hands.  What is the real external world to the man of science?  It is the world of atoms and molecules, of minuter touch things that he cannot actually touch, but which he conceives as though he could touch them.

It should be observed that the man of science has no right to deny the real world which is revealed in the experience of the plain man.  In all his dealings with the things which interest him in common life, he refers to this world just as the plain man does.  He sees a tree and walks towards it, and distinguishes between its real and its apparent color, its real and its apparent size.  He talks about seeing things as they are, or not seeing things as they are.  These distinctions in his experience of things remain even after he has come to believe in atoms and molecules.