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The concurrent experience of all other Men with ours, produces assurance approaching to Knowledge.
      §6. Concerning the first of these, viz. particular matter of fact,
      First, Where any particular thing, consonant to the constant
Observation of our selves and others, in the like case, comes attested
by the concurrent Reports of all that mention it, we receive it as
easily, and build as firmly upon it, as if it were certain Knowledge;
and we reason and act thereupon with as little doubt, as if it were
perfect demonstration. Thus, if all English-men, who have occasion
to mention it, should affirm, that it froze in England the last Winter,
or that there were Swallows seen there in the Summer, I think a Man
could almost as little doubt of it, as that Seven and Four are Eleven.
The first therefore, and highest degree of Probability, is, when the
general consent of all Men, in all Ages, as far as it can be known,
concurrs with a Man’s constant and never-failing Experience in
like cases, to confirm the Truth of any particular matter of fact
attested by fair Witnesses: such are all the stated Constitutions and
Properties of Bodies, and the regular proceedings of Causes and
Effects in the ordinary course of Nature. This we call an Argument
from the nature of Things themselves. For what our own and other
Men’s constant Observation has found always to be after the same
manner, that we with reason conclude to be the Effects of steady
and regular Causes, though they come not within the reach of our
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Knowledge. Thus, That Fire warmed a Man, made Lead fluid, and
changed the colour or consistency in Wood or Charcoal: that Iron
sunk in Water, and swam in Quicksilver: These and the like
Propositions about particular facts, being agreeable to our constant
Experience, as often as we have to do with these matters; and being
generally spoke of, (when mentioned by others,) as things found
constantly to be so, and therefore not so much as controverted by
any body, we are put past doubt, that a relation affirming any such
thing to have been, or any predication that it will happen again in
the same manner, is very true. These Probabilities rise so near to
Certainty, that they govern our Thoughts as absolutely, and influence
all our Actions as fully, as the most evident demonstration: and in
what concerns us, we make little or no difference between them and
certain Knowledge: our Belief thus grounded, rises to Assurance.
Locke Hum IV, 16, §6, pp. 661-662