Philosophy

Selections from the Principles of Philosophy

Rene Descartes

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Meanwhile, that it may be seen wherein I think I have already
promoted the general good, I will here mention the fruits that may
be gathered from my Principles. The first is the satisfaction which
the mind will experience on finding in the work many truths before
unknown; for although frequently truth does not so greatly affect
our imagination as falsity and fiction, because it seems less
wonderful and is more simple, yet the gratification it affords is
always more durable and solid. The second fruit is, that in studying
these principles we will become accustomed by degrees to judge
better of all the things we come in contact with, and thus be made
wiser, in which respect the effect will be quite the opposite of the
common philosophy, for we may easily remark in those we call pedants
that it renders them less capable of rightly exercising their reason
than they would have been if they had never known it. The third is,
that the truths which they contain, being highly clear and certain,
will take away all ground of dispute, and thus dispose men's minds
to gentleness and concord; whereas the contrary is the effect of the
controversies of the schools, which, as they insensibly render those
who are exercised in them more wrangling and opinionative, are
perhaps the prime cause of the heresies and dissensions that now
harass the world. The last and chief fruit of these Principles is,
that one will be able, by cultivating them, to discover many truths
I myself have not unfolded, and thus passing by degrees from one to
another, to acquire in course of time a perfect knowledge of the
whole of philosophy, and to rise to the highest degree of wisdom.
For just as all the arts, though in their beginnings they are rude
and imperfect, are yet gradually perfected by practice, from their
containing at first something true, and whose effect experience
evinces; so in philosophy, when we have true principles, we cannot
fail by following them to meet sometimes with other truths; and we
could not better prove the falsity of those of Aristotle, than by
saying that men made no progress in knowledge by their means during
the many ages they prosecuted them.

I well know that there are some men so precipitate and accustomed to
use so little circumspection in what they do, that, even with the
most solid foundations, they could not rear a firm superstructure;
and as it is usually those who are the readiest to make books, they
would in a short time mar all that I have done, and introduce
uncertainty and doubt into my manner of philosophizing, from which I
have carefully endeavoured to banish them, if people were to receive
their writings as mine, or as representing my opinions. I had, not
long ago, some experience of this in one of those who were believed
desirous of following me the most closely, [Footnote: Regius; see La
Vie de M. Descartes, reduite en abrege (Baillet). Liv. vii., chap.
vii.--T.] and one too of whom I had somewhere said that I had such
confidence in his genius as to believe that he adhered to no
opinions which I should not be ready to avow as mine; for he last
year published a book entitled "Fundamental Physics," in which,
although he seems to have written nothing on the subject of Physics
and Medicine which he did not take from my writings, as well from
those I have published as from another still imperfect on the nature
of animals, which fell into his hands; nevertheless, because he has
copied them badly, and changed the order, and denied certain
metaphysical truths upon which all Physics ought to be based, I am
obliged wholly to disavow his work, and here to request readers not
to attribute to me any opinion unless they find it expressly stated
in my own writings, and to receive no opinion as true, whether in my
writings or elsewhere, unless they see that it is very clearly
deduced from true principles. I well know, likewise, that many ages
may elapse ere all the truths deducible from these principles are
evolved out of them, as well because the greater number of such as
remain to be discovered depend on certain particular experiments
that never occur by chance, but which require to be investigated
with care and expense by men of the highest intelligence, as because
it will hardly happen that the same persons who have the sagacity to
make a right use of them, will possess also the means of making
them, and also because the majority of the best minds have formed so
low an estimate of philosophy in general, from the imperfections
they have remarked in the kind in vogue up to the present time, that
they cannot apply themselves to the search after truth.

But, in conclusion, if the difference discernible between the
principles in question and those of every other system, and the
great array of truths deducible from them, lead them to discern the
importance of continuing the search after these truths, and to
observe the degree of wisdom, the perfection and felicity of life,
to which they are fitted to conduct us, I venture to believe that
there will not be found one who is not ready to labour hard in so
profitable a study, or at least to favour and aid with all his might
those who shall devote themselves to it with success.

The height of my wishes is, that posterity may sometime behold the
happy issue of it, etc.



TO THE MOST SERENE PRINCESS,

ELIZABETH, ELDEST DAUGHTER OF FREDERICK, KING OF BOHEMIA, COUNT
PALATINE, AND ELECTOR OF THE SACRED ROMAN EMPIRE.

MADAM,--The greatest advantage I have derived from the writings
which I have already published, has arisen from my having, through
means of them, become known to your Highness, and thus been
privileged to hold occasional converse with one in whom so many rare
and estimable qualities are united, as to lead me to believe I
should do service to the public by proposing them as an example to
posterity. It would ill become me to flatter, or to give expression
to anything of which I had no certain knowledge, especially in the
first pages of a work in which I aim at laying down the principles
of truth. And the generous modesty that is conspicuous in all your
actions, assures me that the frank and simple judgment of a man who
only writes what he believes will be more agreeable to you than the
ornate laudations of those who have studied the art of compliment.
For this reason, I will give insertion to nothing in this letter for
which I have not the certainty both of experience and reason; and in
the exordium, as in the rest of the work, I will write only as
becomes a philosopher. There is a vast difference between real and
apparent virtues; and there is also a great discrepancy between
those real virtues that proceed from an accurate knowledge of the
truth, and such as are accompanied with ignorance or error. The
virtues I call apparent are only, properly speaking, vices, which,
as they are less frequent than the vices that are opposed to them,
and are farther removed from them than the intermediate virtues, are
usually held in higher esteem than those virtues. Thus, because
those who fear dangers too much are more numerous than they who fear
them too little, temerity is frequently opposed to the vice of
timidity, and taken for a virtue, and is commonly more highly
esteemed than true fortitude. Thus, also, the prodigal are in
ordinary more praised than the liberal; and none more easily acquire
a great reputation for piety than the superstitious and
hypocritical. With regard to true virtues, these do not all proceed
from true knowledge, for there are some that likewise spring from
defect or error; thus, simplicity is frequently the source of
goodness, fear of devotion, and despair of courage. The virtues that
are thus accompanied with some imperfections differ from each other,
and have received diverse appellations. But those pure and perfect
virtues that arise from the knowledge of good alone are all of the
same nature, and may be comprised under the single term wisdom. For,
whoever owns the firm and constant resolution of always using his
reason as well as lies in his power, and in all his actions of doing
what he judges to be best, is truly wise, as far as his nature
permits; and by this alone he is just, courageous, temperate, and
possesses all the other virtues, but so well balanced as that none
of them appears more prominent than another: and for this reason,
although they are much more perfect than the virtues that blaze
forth through the mixture of some defect, yet, because the crowd
thus observes them less, they are not usually extolled so highly.
Besides, of the two things that are requisite for the wisdom thus
described, namely, the perception of the understanding and the
disposition of the will, it is only that which lies in the will
which all men can possess equally, inasmuch as the understanding of
some is inferior to that of others. But although those who have only
an inferior understanding may be as perfectly wise as their nature
permits, and may render themselves highly acceptable to God by their
virtue, provided they preserve always a firm and constant resolution
to do all that they shall judge to be right, and to omit nothing
that may lead them to the knowledge of the duties of which they are
ignorant; nevertheless, those who preserve a constant resolution of
performing the right, and are especially careful in instructing
themselves, and who possess also a highly perspicacious intellect,
arrive doubtless at a higher degree of wisdom than others; and I see
that these three particulars are found in great perfection in your
Highness. For, in the first place, your desire of self-instruction
is manifest, from the circumstance that neither the amusements of
the court, nor the accustomed mode of educating ladies, which
ordinarily condemns them to ignorance, have been sufficient to
prevent you from studying with much care all that is best in the
arts and sciences; and the incomparable perspicacity of your
intellect is evinced by this, that you penetrated the secrets of the
sciences and acquired an accurate knowledge of them in a very short
period. But of the vigour of your intellect I have a still stronger
proof, and one peculiar to myself, in that I have never yet met any
one who understood so generally and so well as yourself all that is
contained in my writings. For there are several, even among men of
the highest intellect and learning, who find them very obscure. And
I remark, in almost all those who are versant in Metaphysics, that
they are wholly disinclined from Geometry; and, on the other hand,
that the cultivators of Geometry have no ability for the
investigations of the First Philosophy: insomuch that I can say with
truth I know but one mind, and that is your own, to which both
studies are alike congenial, and which I therefore, with propriety,
designate incomparable. But what most of all enhances my admiration
is, that so accurate and varied an acquaintance with the whole
circle of the sciences is not found in some aged doctor who has
employed many years in contemplation, but in a Princess still young,
and whose countenance and years would more fitly represent one of
the Graces than a Muse or the sage Minerva. In conclusion, I not
only remark in your Highness all that is requisite on the part of
the mind to perfect and sublime wisdom, but also all that can be
required on the part of the will or the manners, in which benignity
and gentleness are so conjoined with majesty that, though fortune
has attacked you with continued injustice, it has failed either to
irritate or crush you. And this constrains me to such veneration
that I not only think this work due to you, since it treats of
philosophy which is the study of wisdom, but likewise feel not more
zeal for my reputation as a philosopher than pleasure in subscribing
myself,--

Of your most Serene Highness, The most devoted servant,

DESCARTES.


OF THE PRINCIPLES OF HUMAN KNOWLEDGE.

 I. THAT in order to seek truth, it is necessary once in the course
of our life, to doubt, as far as possible, of all things.

As we were at one time children, and as we formed various judgments
regarding the objects presented to our senses, when as yet we had
not the entire use of our reason, numerous prejudices stand in the
way of our arriving at the knowledge of truth; and of these it seems
impossible for us to rid ourselves, unless we undertake, once in our
lifetime, to doubt of all those things in which we may discover even
the smallest suspicion of uncertainty.

 II. That we ought also to consider as false all that is doubtful.

Moreover, it will be useful likewise to esteem as false the things
of which we shall be able to doubt, that we may with greater
clearness discover what possesses most certainty and is the easiest
to know.

 III. That we ought not meanwhile to make use of doubt in the
conduct of life.

In the meantime, it is to be observed that we are to avail ourselves
of this general doubt only while engaged in the contemplation of
truth. For, as far as concerns the conduct of life, we are very
frequently obliged to follow opinions merely probable, or even
sometimes, though of two courses of action we may not perceive more
probability in the one than in the other, to choose one or other,
seeing the opportunity of acting would not unfrequently pass away
before we could free ourselves from our doubts.

 IV. Why we may doubt of sensible things.

Accordingly, since we now only design to apply ourselves to the
investigation of truth, we will doubt, first, whether of all the
things that have ever fallen under our senses, or which we have ever
imagined, any one really exist; in the first place, because we know
by experience that the senses sometimes err, and it would be
imprudent to trust too much to what has even once deceived us;
secondly, because in dreams we perpetually seem to perceive or
imagine innumerable objects which have no existence. And to one who
has thus resolved upon a general doubt, there appear no marks by
which he can with certainty distinguish sleep from the waking state.

 V. Why we may also doubt of mathematical demonstrations.

We will also doubt of the other things we have before held as most
certain, even of the demonstrations of mathematics, and of their
principles which we have hitherto deemed self-evident; in the first
place, because we have sometimes seen men fall into error in such
matters, and admit as absolutely certain and self evident what to us
appeared false, but chiefly because we have learnt that God who
created us is all-powerful; for we do not yet know whether perhaps
it was his will to create us so that we are always deceived, even in
the things we think we know best: since this does not appear more
impossible than our being occasionally deceived, which, however, as
observation teaches us, is the case. And if we suppose that an all-
powerful God is not the author of our being, and that we exist of
ourselves or by some other means, still, the less powerful we
suppose our author to be, the greater reason will we have for
believing that we are not so perfect as that we may not be
continually deceived.

 VI. That we possess a free-will, by which we can withhold our
assent from what is doubtful, and thus avoid error.

But meanwhile, whoever in the end may be the author of our being,
and however powerful and deceitful he may be, we are nevertheless
conscious of a freedom, by which we can refrain from admitting to a
place in our belief aught that is not manifestly certain and
undoubted, and thus guard against ever being deceived.

 VII. That we cannot doubt of our existence while we doubt, and that
this is the first knowledge we acquire when we philosophize in
order.

While we thus reject all of which we can entertain the smallest
doubt, and even imagine that it is false, we easily indeed suppose
that there is neither God, nor sky, nor bodies, and that we
ourselves even have neither hands nor feet, nor, finally, a body;
but we cannot in the same way suppose that we are not while we doubt
of the truth of these things; for there is a repugnance in
conceiving that what thinks does not exist at the very time when it
thinks. Accordingly, the knowledge, _I_ THINK, THEREFORE _I_ AM, is
the first and most certain that occurs to one who philosophizes
orderly.

 VIII. That we hence discover the distinction between the mind and
the body, or between a thinking and corporeal thing.

And this is the best mode of discovering the nature of the mind, and
its distinctness from the body: for examining what we are, while
supposing, as we now do, that there is nothing really existing apart
from our thought, we clearly perceive that neither extension, nor
figure, nor local motion,[Footnote: Instead of "local motion," the
French has "existence in any place."] nor anything similar that can
be attributed to body, pertains to our nature, and nothing save
thought alone; and, consequently, that the notion we have of our
mind precedes that of any corporeal thing, and is more certain,
seeing we still doubt whether there is any body in existence, while
we already perceive that we think.

 IX. What thought (COGITATIO) is.

By the word thought, I understand all that which so takes place in
us that we of ourselves are immediately conscious of it; and,
accordingly, not only to understand (INTELLIGERE, ENTENDRE), to will
(VELLE), to imagine (IMAGINARI), but even to perceive (SENTIRE,
SENTIR), are here the same as to think (COGITARE, PENSER). For if I
say, I see, or, I walk, therefore I am; and if I understand by
vision or walking the act of my eyes or of my limbs, which is the
work of the body, the conclusion is not absolutely certain, because,
as is often the case in dreams, I may think that I see or walk,
although I do not open my eyes or move from my place, and even,
perhaps, although I have no body: but, if I mean the sensation
itself, or consciousness of seeing or walking, the knowledge is
manifestly certain, because it is then referred to the mind, which
alone perceives or is conscious that it sees or walks. [Footnote: In
the French, "which alone has the power of perceiving, or of being
conscious in any other way whatever."]

 X. That the notions which are simplest and self-evident, are
obscured by logical definitions; and that such are not to be
reckoned among the cognitions acquired by study, [but as born with
us].

I do not here explain several other terms which I have used, or
design to use in the sequel, because their meaning seems to me
sufficiently self-evident. And I frequently remarked that
philosophers erred in attempting to explain, by logical definitions,
such truths as are most simple and self-evident; for they thus only
rendered them more obscure. And when I said that the proposition,
_I_ THINK, THEREFORE _I_ AM, is of all others the first and most
certain which occurs to one philosophizing orderly, I did not
therefore deny that it was necessary to know what thought,
existence, and certitude are, and the truth that, in order to think
it is necessary to be, and the like; but, because these are the most
simple notions, and such as of themselves afford the knowledge of
nothing existing, I did not judge it proper there to enumerate them.

 XI. How we can know our mind more clearly than our body.

But now that it may be discerned how the knowledge we have of the
mind not only precedes, and has greater certainty, but is even
clearer, than that we have of the body, it must be remarked, as a
matter that is highly manifest by the natural light, that to nothing
no affections or qualities belong; and, accordingly, that where we
observe certain affections, there a thing or substance to which
these pertain, is necessarily found. The same light also shows us
that we know a thing or substance more clearly in proportion as we
discover in it a greater number of qualities. Now, it is manifest
that we remark a greater number of qualities in our mind than in any
other thing; for there is no occasion on which we know anything
whatever when we are not at the same time led with much greater
certainty to the knowledge of our own mind. For example, if I judge
that there is an earth because I touch or see it, on the same
ground, and with still greater reason, I must be persuaded that my
mind exists; for it may be, perhaps, that I think I touch the earth
while there is one in existence; but it is not possible that I
should so judge, and my mind which thus judges not exist; and the
same holds good of whatever object is presented to our mind.
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