properties light, color, and sound, which we believe to be without us, are
merely internal phenomena dependent on outer and inner motions, but with no
resemblance to them. Memory consists in the lingering effects or residuary
traces of perception; it is a sense or consciousness of having felt before
_(sentire se sensisse meminisse est_), and ideas are distinguished from
sensations as the perfect from the present tense. Experience is the
totality of perceptions retained in memory, together with a certain
foresight of the future after the analogy of the past. These stages of
cognition, which can yield prudence but not necessary and universal
knowledge, are present in animals as well as men. The human capacity for
science is dependent on the faculty of speech; words are conventional
signs to facilitate the retention and communication of ideas. As the
memory-images denoted by words are weaker, fainter, and less clearly
discriminated than the original sensations, it comes to pass that a number
of similar ideas of memory receive a common name. Thus abstract general
ideas and generic concepts arise, to which nothing real corresponds, for
in reality particulars alone exist. The universal is a human artefact. The
combination of words into propositions, being an addition or subtraction
of arbitrary symbols or marks, is called judgment; the combination of
propositions into syllogisms, inference; the united body of true or
demonstrated principles, science--hence mathematics is the type of all
knowledge. In short, thought is nothing but calculation and the words with
which we operate are mere counters; he who takes counters for coin is a
fool. Animals lack reason, _i.e._, this power of combining artificial
symbols.

Hobbes's theory of the will is characterized by the same! sensationalism
and mechanism as his theory of knowledge. All spiritual events originate
in impressions of sense. Man responds to the action of objects by a double
reaction, adding to the theoretical reaction of sensation a practical one