It is interesting to see how a man of science, whose reflections compel him to deny the existence of the external world that we all seem to perceive and that we somehow recognize as distinct from anything in our minds, is nevertheless compelled to admit the existence of this world at every turn.

But if we do admit it, what shall we make of it?  Shall we deny the truth of what the psychologist has to tell us about a knowledge of things only through the sensations to which they give rise?  We cannot, surely, do that.  Shall we affirm that we know the external world directly, and at the same time that we do not know it directly, but only indirectly, and through the images which arise in our minds?  That seems inconsistent.  Certainly there is material for reflection here.

Nevertheless the more we reflect on that material, the more evident does it become that the plain man cannot be wrong in believing in the external world which seems revealed in his experiences.  We find that all attempts to discredit it rest upon the implicit assumption of its existence, and fall to the ground when that existence is honestly denied.  So our problem changes its form.  We no longer ask:  Is there an external world? but rather:  What is the external world, and how does it differ from the world of mere ideas?

[1] “The Grammar of Science,” 2d Ed., London, 1900, pp. 60-63.

CHAPTER IV

SENSATIONS AND “THINGS”

15.  SENSE AND IMAGINATION.—­Every one distinguishes between things perceived and things only imagined.  With open eyes I see the desk before me; with eyes closed, I can imagine it.  I lay my hand on it and feel it; I can, without laying my hand on it, imagine that I feel it.  I raise my eyes, and see the pictures on the wall opposite me; I can sit here and call before my mind the image of the door by which the house is entered.

What is the difference between sense and imagination?  It must be a difference of which we are all somehow conscious, for we unhesitatingly distinguish between the things we perceive and the things we merely imagine.

It is well to remember at the outset that the two classes of experiences are not wholly different.  The blue color that I imagine seems blue.  It does not lose this quality because it is only imaginary.  The horse that I imagine seems to have four legs, like a horse perceived.  As I call it before my mind, it seems as large as the real horse.  Neither the color, nor the size, nor the distribution of parts, nor any other attribute of the sort appears to be different in the imaginary object from what it is in the object as given in sensation.

The two experiences are, nevertheless, not the same; and every one knows that they are not the same.  One difference that roughly marks out the two classes of experiences from one another is that, as a rule, our sense-experiences are more vivid than are the images that exist in the imagination.