BOOK I PART II
it pleases; whenever it dispatches the spirits
into that region of the brain, in which the idea
is placed; these spirits always excite the idea,
when they run precisely into the proper traces,
and rummage that cell, which belongs to the
idea. But as their motion is seldom direct, and
naturally turns a little to the one side or the
other; for this reason the animal spirits, falling
into the contiguous traces, present other re-
lated ideas in lieu of that, which the mind de-
sired at first to survey. This change we are
not always sensible of; but continuing still the
same train of thought, make use of the related
idea, which is presented to us, and employ it
in our reasoning, as if it were the same with
what we demanded. This is the cause of many
mistakes and sophisms in philosophy; as will
naturally be imagined, and as it would be easy
to show, if there was occasion.