Still, again, I may withdraw from the fire.  Its heat seems to be diminished.  Has the fire really grown less hot?  And if I could withdraw to a sufficient distance, I know that the fire would appear to me smaller and less bright.  Could I get far enough away to make it seem the faintest speck in the field of vision, would I be tempted to claim that the fire shrunk and grew faint merely because I walked away from it?  Surely not.

Now, suppose that I stand on the same spot and look at the fire without turning my head.  The stick at which I am gazing catches the flame, blazes up, turns red, and finally falls together, a little mass of gray ashes.  Shall I describe this by saying that my sensations have changed, or may I say that the fire itself has changed?  The plain man and the philosopher alike use the latter expression in such a case as this.

Let us take another illustration.  I walk towards the distant house on the plain before me.  What I see as my goal seems to grow larger and brighter.  It does not occur to me to maintain that the house changes as I advance.  But, at a given instant, changes of a different sort make their appearance.  Smoke arises, and flames burst from the roof.  Now I have no hesitation in saying that changes are taking place in the house.  It would seem foolish to describe the occurrence as a mere change in my sensations.  Before it was my sensations that changed; now it is the house itself.

We are drawing this distinction between changes in our sensations and changes in things at every hour in the day.  I cannot move without making things appear and disappear.  If I wag my head, the furniture seems to dance, and I regard it as a mere seeming.  I count on the clock’s going when I no longer look upon its face.  It would be absurd to hold that the distinction is a mere blunder, and has no foundation in our experience.  The role it plays is too important for that.  If we obliterate it, the real world of material things which seems to be revealed in our experience melts into a chaos of fantastic experiences whose appearances and disappearances seem to be subject to no law.

And it is worthy of remark that it is not merely in common life that the distinction is drawn.  Every man of science must give heed to it.  The psychologist does, it is true, pay much attention to sensations; but even he distinguishes between the sensations which he is studying and the material things to which he relates them, such as brains and sense-organs.  And those who cultivate the physical sciences strive, when they give an account of things and their behavior, to lay before us a history of changes analogous to the burning of the stick and of the house, excluding mere changes in sensations.