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First, Doubtful Propositions taken for Principles.
      §8. First, The first and firmest ground of Probability, is the con-
formity any thing has to our own Knowledge; especially that part of
our Knowledge which we have embraced, and continue to look on
as Principles. These have so great an influence upon our Opinions,
that ’tis usually by them we judge of Truth, and measure Prob-
ability, to that degree, that what is inconsistent with our Principles,
is so far from passing for probable with us, that it will not be allowed
possible. The reverence is born to these Principles is so great, and
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their Authority so paramount to all other, that the Testimony not
only of other Men, but the Evidence of our own Senses are often
rejected, when they offer to vouch any thing contrary to these
established Rules. How much the Doctrine of innate Principles, and
that Principles are not to be proved or questioned, has contributed
to this, I will not here examine. This I readily grant, that one Truth
cannot contradict another: but withal I take leave also to say, that
every one ought very carefully to beware what he admits for a
Principle, to examine it strictly, and see whether he certainly knows
it to be true of it self by its own Evidence, or whether he does only
with assurance believe it to be so, upon the Authority of others.
For he hath a strong biass put into his Understanding, which will
unavoidably misguide his Assent, who hath imbibed wrong Prin-
ciples, and has blindly given himself up to the Authority of any
Locke Hum IV, 20, §8, pp. 711-712