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.