From this it will appear, that for man to think and to reflect, is to
feel, or perceive within himself the impressions, the sensations, the
ideas, which have been furnished to his brain by those objects which
give impulse to his senses, with the various changes which his brain
produced on itself in consequence.

_Memory_ is the faculty which the brain has of renewing in itself the
modifications it has received, or rather, to restore itself to a state
similar to that in which it has been placed by the sensations, the
perceptions, the ideas, produced by exterior objects, in the exact order
it received them, without any new action on the part of these objects,
or even when these objects are absent; the brain perceives that these
modifications assimilate with those it formerly experienced in the
presence of the objects to which it relates, or attributes them. Memory
is faithful, when these modifications are precisely the same; it is
treacherous, when they differ from those which the organs have
exteriorly experienced.

_Imagination_ in man is only the faculty which the brain has of
modifying itself, or of forming to itself new perceptions, upon the
model of those which it has anteriorly received through the action of
exterior objects on the senses. The brain, then, does nothing more than
combine ideas which it has already formed, which it recalls to itself,
from which it forms a whole, or a collection of modifications, which it
has not received, which exists no-where but in itself, although the
individual ideas, or the parts of which this ideal whole is composed,
have been previously communicated to it, in consequence of the impulse
given to the senses by exterior objects: it is thus man forms to himself
the idea of _centaurs_, or a being composed of a man and a horse, of
_hyppogriffs_, or a being composed of a horse with wings and a griffin,