— 605 —
They prove not the Existence of Things without us.
      §14. 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 it self, and of its Distinction
from others; about which, we cannot be mistaken whilst they are
in our Minds, though we may, and often are mistaken, when we
retain the Names without the Ideas; or use them confusedly some-
times for one, and sometimes for another Idea. In which cases, the
force of these Axioms reaching only to the Sound, and not the Signi-
fication of the Words, serves only to lead us into Confusion, Mis-
take, and Errour. ’Tis to shew Men, that these Maxims, however
cry’d up for the great guards to Truth, will not secure them from
Errour 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, ’tis in vain to endeavour, nor
would 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 Errours.
Locke Hum IV, 7, §14, p. 605