ernal body. For it will readily be allowed, that the several
instances we have of the conjunction of resembling causes and effects
are in themselves entirely independent, and that the communication
of motion, which I see result at present from the shock of two
billiard-balls, is totally distinct from that which I saw result from
such an impulse a twelve-month ago. These impulses have no influence
on each other. They are entirely divided by time and place; and the one
might have existed and communicated motion, though the other never had
been in being.

There is, then, nothing new either discovered or produced in any objects
by their constant conjunction, and by the uninterrupted resemblance
of their relations of succession and contiguity. But it is from this
resemblance, that the ideas of necessity, of power, and of efficacy, are
derived. These ideas, therefore, represent not anything, that does or
can belong to the objects, which are constantly conjoined. This is
an argument, which, in every view we can examine it, will be found
perfectly unanswerable. Similar instances are still the first source
of our idea of power or necessity; at the same time that they have no
influence by their similarity either on each other, or on any external
object. We must, therefore, turn ourselves to some other quarter to seek
the origin of that idea.

Though the several resembling instances, which give rise to the idea of
power, have no influence on each other, and can never produce any new
quality in the object, which can be the model of that idea, yet the
observation of this resemblance produces a new impression in the mind,
which is its real model. For after we have observed the resemblance in
a sufficient number of instances, we immediately feel a determination of
the mind to pass from one object to its usual attendant, and to conceive
it in a stronger light upon account of that relation. This determination
is the only effect of the resemblance; and therefore must be the same
with power or efficacy, whose idea is derived from the resemblance. The
several instances of resembling conjunctions lead us into the notion of
power and necessity. These instances are in themselves totally distinct
from each other, and have no union but in the mind, which observes
them, and collects their ideas. Necessity, then, is the effect of this
observation, and is nothing but an internal impression of the mind,
or a determination to carry our thoughts fro