shifted in such a manner that no two events bore any resemblance to each
other, but every object was entirely new, without any similitude to
whatever had been seen before, we should never, in that case, have
attained the least idea of necessity, or of a connexion among these
objects. We might say, upon such a supposition, that one object or event
has followed another; not that one was produced by the other. The
relation of cause and effect must be utterly unknown to mankind.
Inference and reasoning concerning the operations of nature would, from
that moment, be at an end; and the memory and senses remain the only
canals, by which the knowledge of any real existence could possibly have
access to the mind. Our idea, therefore, of necessity and causation
arises entirely from the uniformity observable in the operations of
nature, where similar objects are constantly conjoined together, and the
mind is determined by custom to infer the one from the appearance of the
other. These two circumstances form the whole of that necessity, which
we ascribe to matter. Beyond the constant _conjunction_ of similar
objects, and the consequent _inference_ from one to the other, we have
no notion of any necessity or connexion.

If it appear, therefore, that all mankind have ever allowed, without any
doubt or hesitation, that these two circumstances take place in the
voluntary actions of men, and in the operations of mind; it must follow,
that all mankind have ever agreed in the doctrine of necessity, and that
they have hitherto disputed, merely for not understanding each other.

65. As to the first circumstance, the constant and regular conjunction
of similar events, we may possibly satisfy ourselves by the following
considerations. It is universally acknowledged that there is a great
uniformity among the actions of men, in all nations and ages, and that
human nature remains still the same, in its principles and operations.