Within the last two centuries some notions were advanced in logic and
metaphysics, which were taken to be new; and Descartes, Leibnitz,
Mallebranche, and Locke, were regarded as innovators, although nothing
be put forth in their works, but what is clearly laid down in those of
the ancients.
Descartes sets forth, as a first principle, that whoever searches for
truth, ought once in his lifetime at least to doubt of every thing. He
then lays down the four following rules, wherein consists the whole of
his logic.--1. Never to admit any thing as true, but what we evidently
discern to be so; that is, we should carefully avoid rashness and
prejudice, and assent to nothing, till it present itself so clearly to
the mind, that there be no occasion to hesitate about it.--2. To reduce
every difficulty into as many separate parts, as may be necessary to
come at its solution.--3. So to arrange our thoughts, that we may
gradually arise from the more simple and obvious, to the more complex
and remote, adhering to the order wherein they naturally precede one
another.--4. To take so extensive a view of our subject, and be so exact
in the enumeration of its parts, that nothing may escape our
observation.
The first of these principles of doubt and circumspection, so boasted of
in Descartes, is clearly laid down by Aristotle, and forcibly
recommended by the very arguments that Descartes assumes. “Whoever seeks
after instruction,” says Aristotle, “ought first of all to learn to
doubt; for that simplicity of mind, which accompanies hesitation,
contributes to the discovery of truth:” and, “whoever searches for
truth, without beginning his investigation by doubting of every thing,
is like one who wanders he knows not whither, and having no fixed scope,
cannot determine where he is; whilst, on the contrary, he who hath
learned to doubt, so as to inquire, will find, in the end, the place
where he ought to rest.” So, also, speaking of the method to be
observed in our investigations, Aristotle bids us begin always with what
is most evident and best known; and carefully trace to its first
elements and principles whatever is obscure, by properly severing and
defining them.
Descartes imagined he had been the first discoverer of one of the most
proper engines for sapping and demolishing the great bulwark of
scepticism, when he reared even upon doubt itself a basis for truth; for
he looked upon himself as the original advancer of the Enthymem,[275] “I
doubt (or think) therefore I am.” To Descartes has been assigned the
whole honour of this argument, though in reality it is to be found in
St. Augustine. “I do not see,” says that great man, “what mighty force
there is in the scepticism of the academics. For my part, I look upon it
as a very just observation of theirs, that we may deceive ourselves. But
if I deceive myself, may I not thence conclude that I am? For he who has
no existence, cannot deceive himself; wherefore, by that very
circumstance, that I deceive myself, I find that I am.”
Locke, in his “Essay on the Human Understanding,” merely advances the
fruits of an exact attention to the principles of Aristotle, who taught
that all our ideas originally spring from the senses, insomuch that a
blind man can never conceive the idea of colours, nor a deaf man of
sounds; and who makes the senses to convey truth, so far as the
imagination can discern it; and the understanding, so far as truth
regards the conduct of life and morals. It was Aristotle who laid the
foundation of that principle, so celebrated among the Peripatetics, that
“there is nothing in the understanding but what came into it by the
senses.” This principle diffuses itself through his works in a thousand
places, and Locke was singularly indebted for the very foundation of his
system to the Stoics. The basis of his work is, that our sensations are
the materials which reflection makes use of to come at mental notions;
and that our sensations are simple ideas. It is true, that he has thrown
great light upon our manner of acquiring and associating ideas; but the
Stoics reasoned in the very same manner; and if all that they advanced
on this subject, in those works of which we have nothing now remaining
but the titles, had reached our times, we had not needed the labours of
a Locke. There is a most remarkable passage to this point in Plutarch.
He says, “The foundation of the doctrine of Zeno and his school, as to
logic, was, that all our ideas come from sensation. The mind of man at
his birth, say they, is like white paper, adapted to receive whatever
may be written on it. The first impressions that it receives come to it
from the senses: if the objects are at a distance, memory retains those
types of them; and the repetition of these impressions constitutes
experience. Ideas or notions are of two kinds, natural and artificial.
The natural have their source in sensation, or are derived from the
senses; whence they also gave them the name of anticipations: the
artificial are produced by reflection, in beings endowed with reason.”
This passage, and others in Origen, Sextus Empiricus, Diogenes Laertius,
and St. Augustine, may serve to trace the true origin of the principle,
“That there is nothing in the understanding, but what entered into it by
the senses.” It may be observed, that this axiom, so clearly expressed
by the ancient Stoics and Epicureans, and by Locke among the moderns,
has been erroneously attributed by several learned men, especially
Gassendi and Harvey, to Aristotle.
[275] _Enthymem_: an argument consisting only of an antecedent and
consequential proposition; a syllogism, where the major proposition is
suppressed, and only the minor and consequence produced in words.
_Johnson._
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