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Where it is in our power to suspend it.
      §16. As Knowledge, is no more arbitrary than Perception: so,
I think, Assent is no more in our Power than Knowledge. When
the Agreement of any two Ideas appears to our Minds, whether
immediately, or by the Assistance of Reason, I can no more refuse
to perceive, no more avoid knowing it, than I can avoid seeing those
Objects, which I turn my Eyes to, and look on in day-light: And
what upon full Examination I find the most probable, I cannot deny
my Assent to. But though we cannot hinder our Knowledge, where
the Agreement is once perceived; nor our Assent, where the Prob-
ability manifestly appears upon due Consideration of all the Measures
of it: Yet we can hinder both Knowledge and Assent, by stopping our
Enquiry, and not imploying our Faculties in the search of any Truth.
If it were not so, Ignorance, Error, or Infidelity could not in any
Case be a Fault. Thus in some Cases, we can prevent or suspend
our Assent: But can a Man, versed in modern or ancient History,
doubt whether there be such a Place as Rome, or whether there was
such a Man as Julius Caesar? Indeed there are millions of Truths,
that a Man is not, or may not think himself concerned to know; as
whether our King Richard the Third was crook-back’d, or no; or
whether Roger Bacon was a Mathematician, or a Magician. In these
and such like Cases, where the Assent one way or other, is of no
Importance to the Interest of any one, no Action, no Concernment
of his following, or depending thereon, there ’tis not strange, that
the Mind should give it self up to the common Opinion, or render
it self to the first Comer. These and the like Opinions, are of so
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little weight and moment, that like Motes in the Sun, their Tenden-
cies are very rarely taken notice of. They are there, as it were, by
Chance, and the Mind lets them float at liberty. But where the
Mind judges that the Proposition has concernment in it; where
the Assent, or not Assenting is thought to draw Consequences
of Moment after it, and Good or Evil to depend on chusing, or
refusing the right side, and the Mind sets it self seriously to enquire,
and examine the Probability: there, I think, it is not in our Choice,
to take which side we please, if manifest odds appear on either.
The greater Probability, I think, in that Case, will determine the
Assent: and a Man can no more avoid assenting, or taking it to be
true, where he perceives the greater Probability, than he can avoid
knowing it to be true, where he perceives the Agreement or
Disagreement of any two Ideas.
      If this be so, the Foundation of Errour will lie in wrong Measures
of Probability; as the Foundation of Vice in wrong Measures of
Good.
Locke Hum IV, 20, §16, pp. 717-718