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Selections from the Principles of Philosophy

Rene Descartes

LVIII. That number and all universals are only modes of thought.

In the same way number, when it is not considered as in created
things, but merely in the abstract or in general, is only a mode of
thinking; and the same is true of all those general ideas we call
universals.

 LIX. How universals are formed; and what are the five common, viz.,
genus, species, difference, property, and accident.

Universals arise merely from our making use of one and the same idea
in thinking of all individual objects between which there subsists a
certain likeness; and when we comprehend all the objects represented
by this idea under one name, this term likewise becomes universal.
For example, when we see two stones, and do not regard their nature
farther than to remark that there are two of them, we form the idea
of a certain number, which we call the binary; and when we
afterwards see two birds or two trees, and merely take notice of
them so far as to observe that there are two of them, we again take
up the same idea as before, which is, accordingly, universal; and we
likewise give to this number the same universal appellation of
binary. In the same way, when we consider a figure of three sides,
we form a certain idea, which we call the idea of a triangle, and we
afterwards make use of it as the universal to represent to our mind
all other figures of three sides. But when we remark more
particularly that of figures of three sides, some have a right angle
and others not, we form the universal idea of a right-angled
triangle, which being related to the preceding as more general, may
be called species; and the right angle the universal difference by
which right-angled triangles are distinguished from all others; and
farther, because the square of the side which sustains the right
angle is equal to the squares of the other two sides, and because
this property belongs only to this species of triangles, we may call
it the universal property of the species. Finally, if we suppose
that of these triangles some are moved and others not, this will be
their universal accident; and, accordingly, we commonly reckon five
universals, viz., genus, species, difference, property, accident.

 LX. Of distinctions; and first of the real.

But number in things themselves arises from the distinction there is
between them: and distinction is threefold, viz., real, modal, and
of reason. The real properly subsists between two or more
substances; and it is sufficient to assure us that two substances
are really mutually distinct, if only we are able clearly and
distinctly to conceive the one of them without the other. For the
knowledge we have of God renders it certain that he can effect all
that of which we have a distinct idea: wherefore, since we have now,
for example, the idea of an extended and corporeal substance, though
we as yet do not know with certainty whether any such thing is
really existent, nevertheless, merely because we have the idea of
it, we may be assured that such may exist; and, if it really exists,
that every part which we can determine by thought must be really
distinct from the other parts of the same substance. In the same
way, since every one is conscious that he thinks, and that he in
thought can exclude from himself every other substance, whether
thinking or extended, it is certain that each of us thus considered
is really distinct from every other thinking and corporeal
substance. And although we suppose that God united a body to a soul
so closely that it was impossible to form a more intimate union, and
thus made a composite whole, the two substances would remain really
distinct, notwithstanding this union; for with whatever tie God
connected them, he was not able to rid himself of the power he
possessed of separating them, or of conserving the one apart from
the other, and the things which God can separate or conserve
separately are really distinct.

 LXI. Of the modal distinction.

There are two kinds of modal distinctions, viz., that between the
mode properly so-called and the substance of which it is a mode, and
that between two modes of the same substance. Of the former we have
an example in this, that we can clearly apprehend substance apart
from the mode which we say differs from it; while, on the other
hand, we cannot conceive this mode without conceiving the substance
itself. There is, for example, a modal distinction between figure or
motion and corporeal substance in which both exist; there is a
similar distinction between affirmation or recollection and the
mind. Of the latter kind we have an illustration in our ability to
recognise the one of two modes apart from the other, as figure apart
from motion, and motion apart from figure; though we cannot think of
either the one or the other without thinking of the common substance
in which they adhere. If, for example, a stone is moved, and is
withal square, we can, indeed, conceive its square figure without
its motion, and reciprocally its motion without its square figure;
but we can conceive neither this motion nor this figure apart from
the substance of the stone. As for the distinction according to
which the mode of one substance is different from another substance,
or from the mode of another substance, as the motion of one body is
different from another body or from the mind, or as motion is
different from doubt, it seems to me that it should be called real
rather than modal, because these modes cannot be clearly conceived
apart from the really distinct substances of which they are the
modes.

 LXII. Of the distinction of reason (logical distinction).

Finally, the distinction of reason is that between a substance and
some one of its attributes, without which it is impossible, however,
we can have a distinct conception of the substance itself; or
between two such attributes of a common substance, the one of which
we essay to think without the other. This distinction is manifest
from our inability to form a clear and distinct idea of such
substance, if we separate from it such attribute; or to have a clear
perception of the one of two such attributes if we separate it from
the other. For example, because any substance which ceases to endure
ceases also to exist, duration is not distinct from substance except
in thought (RATIONE); and in general all the modes of thinking which
we consider as in objects differ only in thought, as well from the
objects of which they are thought as from each other in a common
object.[Footnote: "and generally all the attributes that lead us to
entertain different thoughts of the same thing, such as, for
example, the extension of body and its property of divisibility, do
not differ from the body which is to us the object of them, or from
each other, unless as we sometimes confusedly think the one without
thinking the other."--FRENCH.] It occurs, indeed, to me that I have
elsewhere classed this kind of distinction with the modal (viz.,
towards the end of the Reply to the First Objections to the
Meditations on the First Philosophy); but there it was only
necessary to treat of these distinctions generally, and it was
sufficient for my purpose at that time simply to distinguish both of
them from the real.

 LXIII. How thought and extension may be distinctly known, as
constituting, the one the nature of mind, the other that of body.

Thought and extension may be regarded as constituting the natures of
intelligent and corporeal substance; and then they must not be
otherwise conceived than as the thinking and extended substances
themselves, that is, as mind and body, which in this way are
conceived with the greatest clearness and distinctness. Moreover, we
more easily conceive extended or thinking substance than substance
by itself, or with the omission of its thinking or extension. For
there is some difficulty in abstracting the notion of substance from
the notions of thinking and extension, which, in truth, are only
diverse in thought itself (i.e., logically different); and a concept
is not more distinct because it comprehends fewer properties, but
because we accurately distinguish what is comprehended in it from
all other notions.

 LXIV. How these may likewise be distinctly conceived as modes of
substance.

Thought and extension may be also considered as modes of substance;
in as far, namely, as the same mind may have many different
thoughts, and the same body, with its size unchanged, may be
extended in several diverse ways, at one time more in length and
less in breadth or depth, and at another time more in breadth and
less in length; and then they are modally distinguished from
substance, and can be conceived not less clearly and distinctly,
provided they be not regarded as substances or things separated from
others, but simply as modes of things. For by regarding them as in
the substances of which they are the modes, we distinguish them from
these substances, and take them for what in truth they are: whereas,
on the other hand, if we wish to consider them apart from the
substances in which they are, we should by this itself regard them
as self-subsisting things, and thus confound the ideas of mode and
substance.

 LXV. How we may likewise know their modes.

In the same way we will best apprehend the diverse modes of thought,
as intellection, imagination, recollection, volition, etc., and also
the diverse modes of extension, or those that belong to extension,
as all figures, the situation of parts and their motions, provided
we consider them simply as modes of the things in which they are;
and motion as far as it is concerned, provided we think merely of
locomotion, without seeking to know the force that produces it, and
which nevertheless I will essay to explain in its own place.

 LXVI. How our sensations, affections, and appetites may be clearly
known, although we are frequently wrong in our judgments regarding
them.

There remain our sensations, affections, and appetites, of which we
may also have a clear knowledge, if we take care to comprehend in
the judgments we form of them only that which is precisely contained
in our perception of them, and of which we are immediately
conscious. There is, however, great difficulty in observing this, at
least in respect of sensations; because we have all, without
exception, from our youth judged that all the things we perceived by
our senses had an existence beyond our thought, and that they were
entirely similar to the sensations, that is, perceptions, we ad of
them. Thus when, for example, we saw a certain colour, we thought we
saw something occupying a place out of us, and which was entirely
similar to that idea of colour we were then conscious of; and from
the habit of judging in this way, we seemed to see this so clearly
and distinctly that we esteemed it (i.e., the externality of the
colour) certain and indubitable.

 LXVII. That we are frequently deceived in our judgments regarding
pain itself.

The same prejudice has place in all our other sensations, even in
those of titillation and pain. For though we are not in the habit of
believing that there exist out of us objects that resemble
titillation and pain, we do not nevertheless consider these
sensations as in the mind alone, or in our perception, but as in the
hand, or foot, or some other part of our body. There is no reason,
however, to constrain us to believe that the pain, for example,
which we feel, as it were, in the foot is something out of the mind
existing in the foot, or that the light which we see, as it were, in
the sun exists in the sun as it is in us. Both these beliefs are
prejudices of our early years, as will clearly appear in the sequel.

 LXVIII. How in these things what we clearly conceive is to be
distinguished from that in which we may be deceived.

But that we may distinguish what is clear in our sensations from
what is obscure, we ought most carefully to observe that we possess
a clear and distinct knowledge of pain, colour, and other things of
this sort, when we consider them simply as sensations or thoughts;
but that, when they are judged to be certain things subsisting
beyond our mind, we are wholly unable to form any conception of
them. Indeed, when any one tells us that he sees colour in a body or
feels pain in one of his limbs, this is exactly the same as if he
said that he there saw or felt something of the nature of which he
was entirely ignorant, or that he did not know what he saw or felt.
For although, when less attentively examining his thoughts, a person
may easily persuade himself that he has some knowledge of it, since
he supposes that there is something resembling that sensation of
colour or of pain of which he is conscious; yet, if he reflects on
what the sensation of colour or pain represents to him as existing
in a coloured body or in a wounded member, he will find that of such
he has absolutely no knowledge.

 LXIX. That magnitude, figure, etc., are known far differently from
colour, pain, etc.

What we have said above will be more manifest; especially if we
consider that size in the body perceived, figure, motion (at least
local, for philosophers by fancying other kinds of motion have
rendered its nature less intelligible to themselves), the situation
of parts, duration, number, and those other properties which, as we
have already said, we clearly perceive in all bodies, are known by
us in a way altogether different from that in which we know what
colour is in the same body, or pain, smell, taste, or any other of
those properties which I have said above must be referred to the
senses. For although when we see a body we are not less assured of
its existence from its appearing figured than from its appearing
coloured,[Footnote: "by the colour we perceive on occasion of it."--
FRENCH.] we yet know with far greater clearness its property of
figure than its colour.

 LXX. That we may judge of sensible things in two ways, by the one
of which we avoid error, by the other fall into it.

It is thus manifest that to say we perceive colours in objects is in
reality equivalent to saying we perceive something in objects and
are yet ignorant of what it is, except as that which determines in
us a certain highly vivid and clear sensation, which we call the
sensation of colours. There is, however, very great diversity in the
manner of judging: for so long as we simply judge that there is an
unknown something in objects (that is, in things such as they are,
from which the sensation reached us), so far are we from falling
into error that, on the contrary, we thus rather provide against it,
for we are less apt to judge rashly of a thing which we observe we
do not know. But when we think we perceive colours in objects,
although we are in reality ignorant of what we then denominate
colour, and are unable to conceive any resemblance between the
colour we suppose to be in objects, and that of which we are
conscious in sensation, yet because we do not observe this, or
because there are in objects several properties, as size, figure,
number, etc., which, as we clearly know, exist, or may exist in them
as they are perceived by our senses or conceived by our
understanding, we easily glide into the error of holding that what
is called colour in objects is something entirely resembling the
colour we perceive, and thereafter of supposing that we have a clear
perception of what is in no way perceived by us.

 LXXI. That the chief cause of our errors is to be found in the
prejudices of our childhood.

And here we may notice the first and chief cause of our errors. In
early life the mind was so closely bound to the body that it
attended to nothing beyond the thoughts by which it perceived the
objects that made impression on the body; nor as yet did it refer
these thoughts to anything existing beyond itself, but simply felt
pain when the body was hurt, or pleasure when anything beneficial to
the body occurred, or if the body was so highly affected that it was
neither greatly benefited nor hurt, the mind experienced the
sensations we call tastes, smells, sounds, heat, cold, light,
colours, and the like, which in truth are representative of nothing
existing out of our mind, and which vary according to the
diversities of the parts and modes in which the body is affected.
[Footnote: "which vary according to the diversities of the movements
that pass from all parts of our body to the part of the brain to
which it (the mind) is closely joined and united."--FRENCH.] The
mind at the same time also perceived magnitudes, figures, motions,
and the like, which were not presented to it as sensations but as
things or the modes of things existing, or at least capable of
existing out of thought, although it did not yet observe this
difference between these two kinds of perceptions. And afterwards
when the machine of the body, which has been so fabricated by nature
that it can of its own inherent power move itself in various ways,
by turning itself at random on every side, followed after what was
useful and avoided what was detrimental; the mind, which was closely
connected with it, reflecting on the objects it pursued or avoided,
remarked, for the first time, that they existed out of itself, and
not only attributed to them magnitudes, figures, motions, and the
like, which it apprehended either as things or as the modes of
things, but, in addition, attributed to them tastes, odours, and the
other ideas of that sort, the sensations of which were caused by
itself; [Footnote: "which it perceived on occasion of them" (i.e.,
of external objects).--FRENCH.] and as it only considered other
objects in so far as they were useful to the body, in which it was
immersed, it judged that there was greater or less reality in each
object, according as the impressions it caused on the body were more
or less powerful. Hence arose the belief that there was more
substance or body in rocks and metals than in air or water, because
the mind perceived in them more hardness and weight. Moreover, the
air was thought to be merely nothing so long as we experienced no
agitation of it by the wind, or did not feel it hot or cold. And
because the stars gave hardly more light than the slender flames of
candles, we supposed that each star was but of this size. Again,
since the mind did not observe that the earth moved on its axis, or
that its superficies was curved like that of a globe, it was on that
account more ready to judge the earth immovable and its surface
flat. And our mind has been imbued from our infancy with a thousand
other prejudices of the same sort which afterwards in our youth we
forgot we had accepted without sufficient examination, and admitted
as possessed of the highest truth and clearness, as if they had been
known by means of our senses, or implanted in us by nature.

 LXXII. That the second cause of our errors is that we cannot forget
these prejudices.

And although now in our mature years, when the mind, being no longer
wholly subject to the body, is not in the habit of referring all
things to it, but also seeks to discover the truth of things
considered in themselves, we observe the falsehood of a great many
of the judgments we had before formed; yet we experience a
difficulty in expunging them from our memory, and, so long as they
remain there, they give rise to various errors. Thus, for example,
since from our earliest years we imagined the stars to be of very
small size, we find it highly difficult to rid ourselves of this
imagination, although assured by plain astronomical reasons that
they are of the greatest,--so prevailing is the power of
preconceived opinion.
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