the statements of logic. As he puts it: "There is no object, which implies the existence of any other
if we consider these objects in themselves, and never look beyond the ideas which we form of
them." Hume argues from this that it must be experience that gives knowledge of cause and effect,
but that it cannot be merely the experience of the two events A and B which are in a causal
relation to each other. It must be experience, because the connection is not logical; and it cannot
be merely the experience of the particular events A and B, since we can discover nothing in A by
itself which should lead it to produce B. The experience required, he says, is that of the constant
conjunction of events of the kind A with events of the kind B. He points out that when, in
experience, two objects are constantly conjoined, we do in fact infer one from the other. (When he
says "infer," he means that perceiving the one makes us expect the other; he does not mean a
formal or explicit inference.) "Perhaps, the necessary connection depends on the inference," not
vice versa. That is to say, the sight of A causes the expectation of B, and so leads us to believe that
there is a necessary connection between A and B. The inference is not determined by reason, since
that would require us to assume the uniformity of nature, which itself is not necessary, but only
inferred from experience.
Hume is thus led to the view that, when we say "A causes B," we mean only that A and B are
constantly conjoined in fact, not that there is some necessary connection between them. "We have
no other notion of cause and effect, but that of certain objects, which have been always conjoined
together.... We cannot penetrate into the reason of the conjunction."
He backs up his theory with a definition of "belief," which is, he maintains, "a lively idea related
to or associated with a present impression." Through association, if A and B have been constantly
conjoined in past experience, the impression of A produces that lively idea of B which constitutes
belief in B. This explains why we believe A and B to be connected: the percept of A is connected
with the idea of B, and so we come to think that A is connected with B, though this opinion is
really groundless. "Objects have no discoverable connexion together; nor is it from any other
principle but custom operating upon the imagination, that we can draw any inference from the
appearance of one to the experience of another." He repeats many