arises from a number of similar instances which occur of the constant
conjunction of these events; nor can that idea ever be suggested by any
one of these instances, surveyed in all possible lights and positions.
But there is nothing in a number of instances, different from every
single instance, which is supposed to be exactly similar; except only,
that after a repetition of similar instances, the mind is carried by
habit, upon the appearance of one event, to expect its usual attendant,
and to believe that it will exist. This connexion, therefore, which we
_feel_ in the mind, this customary transition of the imagination from
one object to its usual attendant, is the sentiment or impression from
which we form the idea of power or necessary connexion. Nothing farther
is in the case. Contemplate the subject on all sides; you will never
find any other origin of that idea. This is the sole difference between
one instance, from which we can never receive the idea of connexion, and
a number of similar instances, by which it is suggested. The first time
a man saw the communication of motion by impulse, as by the shock of two
billiard balls, he could not pronounce that the one event was
_connected:_ but only that it was _conjoined_ with the other. After he
has observed several instances of this nature, he then pronounces them
to be _connected._ What alteration has happened to give rise to this new
idea of _connexion?_ Nothing but that he now _feels_ these events to be
connected in his imagination, and can readily foretell the existence of
one from the appearance of the other. When we say, therefore, that one
object is connected with another, we mean only that they have acquired a
connexion in our thought, and give rise to this inference, by which they
become proofs of each other's existence: A conclusion which is somewhat
extraordinary, but which seems founded on sufficient evidence. Nor will
its evidence be weakened by any general diffidence of the understanding,
or sceptical suspicion concerning every conclusion which is new and
extraordinary. No conclusions can be more agreeable to scepticism than