much of nature as will enable us to attain to the aforesaid character,
and  also to form a social order such as is most conducive to the
attainment of this character by the greatest number with the least
difficulty and danger. 

[15]  (1) We must seek the assistance of Moral Philosophy [d] and
the Theory of Education; further, as health is no insignificant means
for attaining our end, we must also include the whole science of
Medicine, and, as many difficult things are by contrivance rendered
easy, and we can in this way gain much time and convenience, the
science of Mechanics must in no way be despised. 

[16]  (1) But before all things, a means must be devised for
improving the understanding and purifying it, as far as may be at
the outset, so that it may apprehend things without error, and in
the best possible way.  (2) Thus it is apparent to everyone that I
wish to direct all science to one end [e] and aim, so that we may
attain to the supreme human perfection which we have named; and,
therefore, whatsoever in the sciences does not serve to promote
our object will have to be rejected as useless.  (3) To sum up the
matter in a word, all our actions and thoughts must be directed to
this one end. 

[17]  (1) Yet, as it is necessary that while we are endeavoring to
attain our purpose, and bring the understanding into the right path
we should carry on our life, we are compelled first of all to lay
down certain rules of life as provisionally good, to wit the
following:-
I.  (2) To speak in a manner intelligible to the multitude, and to
    comply with every general custom that does not hinder the
    attainment of our purpose.  (3) For we can gain from the multitude
    no small advantages, provided that we strive to accommodate
    ourselves to its understanding as far as possible: moreover,
    we shall in this way gain a friendly audience for the reception
    of the truth. 
II. (17:4) To indulge ourselves with pleasures only in so far as they
    are necessary for preserving health. 
III. (5) Lastly, to endeavor to obtain only sufficient money or other
    commodities to enable us to preserve our life and health, and to
    follow such general customs as are consistent with our purpose.

[18]  (1) Having laid down these preliminary rules, I will betake
myself to the first and most important 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.