We see, thus, that the plain man and the man of science are quite right in accepting the external world.  The objective order is known as directly as is the subjective order.  Both are orders of experiences; they are open to observation, and we have, in general, little difficulty in distinguishing between them, as the illustrations given above amply prove.

18.  THE EXISTENCE OF MATERIAL THINGS.—­One difficulty seems to remain and to call for a solution.  We all believe that material things exist when we no longer perceive them.  We believe that they existed before they came within the field of our observation.

In these positions the man of science supports us.  The astronomer has no hesitation in saying that the comet, which has sailed away through space, exists, and will return.  The geologist describes for us the world as it was in past ages, when no eye was opened upon it.

But has it not been stated above that the material world is an order of experiences? and can there be such a thing as an experience that is not experienced by somebody?  In other words, can the world exist, except as it is perceived to exist?

This seeming difficulty has occasioned much trouble to philosophers in the past.  Bishop Berkeley (1684-1753) said, “To exist is to be perceived.”  There are those who agree with him at the present day.

Their difficulty would have disappeared had they examined with sufficient care the meaning of the word “exist.”  We have no right to pass over the actual uses of such words, and to give them a meaning of our own.  If one thing seems as certain as any other, it is that material things exist when we do not perceive them.  On what ground may the philosopher combat the universal opinion, the dictum of common sense and of science?  When we look into his reasonings, we find that he is influenced by the error discussed at length in the last section—­he has confused the phenomena of the two orders of experience.

I have said that, when we concern ourselves with the objective order, we abstract or should abstract, from the relations which things bear to our senses.  We account for phenomena by referring to other phenomena which we have reason to accept as their physical conditions or causes.  We do not consider that a physical cause is effective only while we perceive it.  When we come back to this notion of our perceiving a thing or not perceiving it, we have left the objective order and passed over to the subjective.  We have left the consideration of “things” and have turned to sensations.

There is no reason why we should do this.  The physical order is an independent order, as we have seen.  The man of science, when he is endeavoring to discover whether some thing or quality of a thing really existed at some time in the past, is not in the least concerned to establish the fact that some one saw it.  No one ever saw the primitive fire-mist from which, as we are told, the world came into being.  But the scientist cares little for that.  He is concerned only to prove that the phenomena he is investigating really have a place in the objective order.  If he decides that they have, he is satisfied; he has proved something to exist. To belong to the objective order is to exist as a physical thing or quality.