BOOK I PART III
conception of the usual effect, and give to that
conception a force and vivacity, which make it
superior to the mere fictions of the fancy. We
may correct this propensity by a reflection on
the nature of those circumstances: but it is still
certain, that custom takes the start, and gives a
biass to the imagination.
To illustrate this by a familiar instance, let us
consider the case of a man, who, being hung
out from a high tower in a cage of iron can-
not forbear trembling, when he surveys the
precipice below him, though he knows himself
to be perfectly secure from falling, by his ex-
perience of the solidity of the iron, which sup-
ports him; and though the ideas of fall and de-
scent, and harm and death, be derived solely
from custom and experience. The same cus-
tom goes beyond the instances, from which it is