On the Improvement of the Understanding | Page 6

task, namely, the amendment of the
understanding, and the rendering it capable of understanding things in
the manner necessary for attaining our end. (2) In order to bring this
about, the natural order demands that I should here recapitulate all the
modes of perception, which I have hitherto employed for affirming or
denying anything with certainty, so that I may choose the best, and at
the same time begin to know my own powers and the nature which I
wish to perfect.
[19] (1) Reflection shows that all modes of perception or knowledge
may be reduced to four:- I. (2) Perception arising from hearsay or from
some sign which everyone may name as he please. II. (3) Perception
arising from mere experience - that is, form experience not yet
classified by the intellect, and only so called because the given event

has happened to take place, and we have no contradictory fact to set
against it, so that it therefore remains unassailed in our minds. III. (19:4)
Perception arising when the essence of one thing is inferred from
another thing, but not adequately; this comes when [f] from some effect
we gather its cause, or when it is inferred from some general
proposition that some property is always present. IV. (5) Lastly, there is
the perception arising when a thing is perceived solely through its
essence, or through the knowledge of its proximate cause.
[20] (1) All these kinds of perception I will illustrate by examples. (2)
By hearsay I know the day of my birth, my parentage, and other matters
about which I have never felt any doubt. (3) By mere experience I
know that I shall die, for this I can affirm from having seen that others
like myself have died, though all did not live for the same period, or die
by the same disease. (4) I know by mere experience that oil has the
property of feeding fire, and water of extinguishing it. (5) In the same
way I know that a dog is a barking animal, man a rational animal, and
in fact nearly all the practical knowledge of life.
[21] (1) We deduce one thing from another as follows: when we clearly
perceive that we feel a certain body and no other, we thence clearly
infer that the mind is united [g] to the body, and that their union is the
cause of the given sensation; but we cannot thence absolutely
understand [h] the nature of the sensation and the union. (2) Or, after I
have become acquainted with the nature of vision, and know that it has
the property of making one and the same thing appear smaller when far
off than when near, I can infer that the sun is larger than it appears, and
can draw other conclusions of the same kind.
[22] (1) Lastly, a thing may be perceived solely through its essence;
when, from the fact of knowing something, I know what it is to know
that thing, or when, from knowing the essence of the mind, I know that
it is united to the body. (2) By the same kind of knowledge we know
that two and three make five, or that two lines each parallel to a third,
are parallel to one another, &c. (3) The things which I have been able
to know by this kind of knowledge are as yet very few.
[23] (1) In order that the whole matter may be put in a clearer light, I

will make use of a single illustration as follows. (2) Three numbers are
given - it is required to find a fourth, which shall be to the third as the
second is to the first. (23:3) Tradesmen will at once tell us that they
know what is required to find the fourth number, for they have not yet
forgotten the rule which was given to them arbitrarily without proof by
their masters; others construct a universal axiom from their experience
with simple numbers, where the fourth number is self-evident, as in the
case of 2, 4, 3, 6; here it is evident that if the second number be
multiplied by the third, and the product divided by the first, the quotient
is 6; when they see that by this process the number is produced which
they knew beforehand to be the proportional, they infer that the process
always holds good for finding a fourth number proportional.
[24] (1) Mathematicians, however, know by the proof of the nineteenth
proposition of the seventh book of Euclid, what numbers are
proportionals, namely, from the nature and property of proportion it
follows that the product of the first and fourth will be equal to the
product of the second and third: still they do not see the adequate
proportionality of the given numbers,