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Selections from the Principles of Philosophy
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.