remote, direct or collateral. Heat and light are collateral effects of
fire, and the one effect may justly be inferred from the other.

23. If we would satisfy ourselves, therefore, concerning the nature of
that evidence, which assures us of matters of fact, we must enquire how
we arrive at the knowledge of cause and effect.

I shall venture to affirm, as a general proposition, which admits of no
exception, that the knowledge of this relation is not, in any instance,
attained by reasonings _a priori_; but arises entirely from experience,
when we find that any particular objects are constantly conjoined with
each other. Let an object be presented to a man of ever so strong
natural reason and abilities; if that object be entirely new to him, he
will not be able, by the most accurate examination of its sensible
qualities, to discover any of its causes or effects. Adam, though his
rational faculties be supposed, at the very first, entirely perfect,
could not have inferred from the fluidity and transparency of water that
it would suffocate him, or from the light and warmth of fire that it
would consume him. No object ever discovers, by the qualities which
appear to the senses, either the causes which produced it, or the
effects which will arise from it; nor can our reason, unassisted by
experience, ever draw any inference concerning real existence and
matter of fact.

24. This proposition, _that causes and effects are discoverable, not by
reason but by experience_, will readily be admitted with regard to such
objects, as we remember to have once been altogether unknown to us;
since we must be conscious of the utter inability, which we then lay
under, of foretelling what would arise from them. Present two smooth
pieces of marble to a man who has no tincture of natural philosophy; he