BOOK I PART III
to its absent cause or effect, is never founded
on any qualities, which we observe in that ob-
ject, considered in itself, or, in other words, that
it is impossible to determine, otherwise than
by experience, what will result from any phe-
nomenon, or what has preceded it. But though
this be so evident in itself, that it seemed not to
require any, proof; yet some philosophers have
imagined that there is an apparent cause for the
communication of motion, and that a reason-
able man might immediately infer the motion
of one body from the impulse of another, with-
out having recourse to any past observation.
That this opinion is false will admit of an easy
proof. For if such an inference may be drawn
merely from the ideas of body, of motion, and
of impulse, it must amount to a demonstration,
and must imply the absolute impossibility of
any contrary supposition. Every effect, then,