To form a precise notion of _thought_, it will be requisite to examine,
step by step, what passes in man during the presence of any object
whatever. Suppose for a moment this object to be a peach: this fruit
makes, at the first view, two different impressions on his eyes; that is
to say, it produces two modifications, which are transmitted to the
brain, which on this occasion experiences two new perceptions, or has
two new ideas or modes of existence, designated by the terms _colour_
and _rotundity_; in consequence, he has an idea of a body possessing
roundness and colour: if he places his hand on this fruit, the organ of
feeling having been set in action, his hand experiences three new
impressions, which are called _softness, coolness, weight_, from whence
result three new perceptions in the brain, he has consequently three new
ideas: if he approximates this peach to his nose, the organ of
_smelling_ receives an impulse, which, communicated to the brain, a new
perception arises, by which he acquires a new idea, called _odour_: if
he carries this fruit to his mouth, the organ of taste becomes affected
in a very lively manner: this impulse communicated to the brain, is
followed by a perception that generates in him the idea of _flavour_. In
re-uniting all these impressions, or these various modifications of his
organs, which it have been consequently transmitted to his brain; that
is to say, in combining the different sensations, perceptions, and
ideas, that result from the impulse he has received, he has an idea of a
whole, which he designates by the name of a peach, with which he can
then occupy his thoughts.

From this it is sufficiently proved that thought has a commencement, a
duration, an end; or rather a generation, a succession, a dissolution,
like all the other modifications of matter; like them, thought is
excited, is determined, is increased, is divided, is compounded, is
simplified, &c. If, therefore, the soul, or the principle that thinks,