14. But they prove not the existence of things without us.
But yet, though both these propositions (as you see)
may be equally demonstrated, viz., that there may be a vacuum, and that there cannot be a vacuum, by these two
certain principles, viz., what is, is, and the same thing cannot be and not be: yet neither of these principles will
serve to prove to us, that any, or what bodies do exist: for that we are left to our senses to discover to us as far as
they can. Those universal and self-evident principles being only our constant, clear, and distinct knowledge of our
own ideas, more general or comprehensive, can assure us of nothing that passes without the mind: their certainty
is founded only upon the knowledge we have of each idea by itself, and of its distinction from others, about which
we cannot be mistaken whilst they are in our minds; though we may be and often are mistaken when we retain the
names without the ideas; or use them confusedly, sometimes for one and sometimes for another idea. In which
cases the force of these axioms, reaching only to the sound, and not the signification of the words, serves only to
lead us into confusion, mistake, and error. It is to show men that these maxims, however cried up for the great
guards of truth, will not secure them from error in a careless loose use of their words, that I have made this
remark. In all that is here suggested concerning their little use for the improvement of knowledge, or dangerous
use in undetermined ideas, I have been far enough from saying or intending they should be laid aside; as some
have been too forward to charge me. I affirm them to be truths, self-evident truths; and so cannot be laid aside. As
far as their influence will reach, it is in vain to endeavour, nor will I attempt, to abridge it. But yet, without any
injury to truth or knowledge, I may have reason to think their use is not answerable to the great stress which
seems to be laid on them; and I may warn men not to make an ill use of them, for the confirming themselves in
errors.
