THE NATURE AND EXTENT OF HUMAN KNOWLEDGE
_Of Truth_
All the ideas which are in God always agree with those things of which
they are the ideas. Therefore, all ideas, in so far as they are related
to God, are true.
A true idea[18] (for we possess a true idea) is something different from
its correlate (_ideatum_); thus a circle is different from the idea of a
circle. The idea of a circle is not something having a circumference and
a center, as a circle has; nor is the idea of a body that body itself.
Now, as it is something different from its correlate, it is capable of
being understood through itself; in other words, the idea, in so far as
its actual essence (_essentia formalis_) is concerned, may be the
subject of another subjective essence. And, again, this second
subjective essence will, regarded in itself, be something real and
capable of being understood; and so on indefinitely. For instance, the
man Peter is something real; the true idea of Peter is the reality of
Peter represented subjectively, and is in itself something real, and
quite distinct from the actual Peter. Now, as this true idea of Peter is
in itself something real, and has its own individual existence, it will
also be capable of being understood--that is, of being the subject of
another idea which will contain by representation all that the idea of
Peter contains actually. And, again, this idea of the idea of Peter has
its own individuality, which may become the subject of yet another idea;
and so on indefinitely. This every one may make trial of for himself, by
reflecting that he knows what Peter is, and also knows that he knows,
and further knows that he knows that he knows, etc. Hence, it is plain
that, in order to understand the actual Peter, it is not necessary first
to understand the idea of Peter, and still less the idea of the idea of
Peter. This is the same as saying that in order to know, there is no
need to know that we know, much less to know that we know that we know.
This is no more necessary than to know the nature of a circle before
knowing the nature of a triangle. But with these ideas the contrary is
the case; for in order to know that I know, I must first know. Hence it
is clear that certainty is nothing else than the subjective essence of a
thing: in other words, the mode in which we perceive an actual reality
is certainty. Further, it is also evident that for the certitude of
truth no further sign is necessary beyond the possession of a true idea;
for, as I have shown, it is not necessary to know that we know that we
know....
He who has a true idea knows at the same time that he has a true idea,
nor can he doubt the truth of the thing. For no one who has a true idea
is ignorant that a true idea involves the highest certitude; to have a
true idea signifying just this, to know a thing perfectly or as well as
possible. No one, in fact, can doubt this, unless he supposes an idea to
be something dumb, like a picture on a tablet, instead of being a mode
of thought, that is to say, intelligence itself. Moreover, I ask who can
know that he understands a thing unless he first of all understands that
thing? that is to say, who can know that he is certain of anything
unless he is first of all certain of that thing? Then, again, what can
be clearer or more certain than a true idea as the standard of truth?
Just as light reveals both itself and the darkness, so truth is the
standard of itself and of the false.
_Of Falsity_
There is nothing positive in ideas which can constitute a form of
falsity. But falsity cannot consist in absolute privation (for we say
that minds and not bodies err and are mistaken); nor can it consist in
absolute ignorance, for to be ignorant and to be in error are different.
Falsehood, therefore, consists in the privation of knowledge which is
involved by inadequate knowledge of things or by inadequate and confused
ideas. For instance, men are deceived because they think themselves
free, and the sole reason for thinking so is that they are conscious of
their own actions, and ignorant of the causes by which those actions are
determined. Their idea of liberty therefore is this--that they know no
cause for their own actions; for as to saying that their actions depend
upon their will, these are words to which no idea is attached. What the
will is, and in what manner it moves the body, every one is ignorant,
for those who pretend otherwise, and devise seats and dwelling-places of
the soul, usually excite our laughter or disgust. Just in the same
manner, when we look at the sun, we imagine its distance from us to be
about 200 feet; the error not consisting solely in the imagination, but
arising from our not knowing what the true distance is when we imagine,
and what are the causes of our imagination. For although we may
afterwards know that the sun is more than 600 diameters of the earth
distant from us, we still imagine it near us, since we imagine it to be
so near, not because we are ignorant of its true distance, but because a
modification of our body involves the essence of the sun, in so far as
our body itself is affected by it.
_The Origin and Nature of Confused Ideas_
The ideas of the modifications of the human body involve the nature both
of external bodies and of the human body itself and must involve the
nature not only of the human body, but of its parts, for the
modifications are ways in which the parts of the human body, and
consequently the whole body, are affected. But an adequate knowledge of
external bodies and of the parts composing the human body does not exist
in God in so far as He is considered as affected by the human mind, but
in so far as He is affected by other ideas. These ideas of
modifications, therefore, in so far as they are related to the human
mind alone, are like conclusions without premises, that is to say, as is
self-evident, they are confused ideas.
The idea which forms the nature of the mind is demonstrated in the same
way not to be clear and distinct when considered in itself. So also with
the idea of the human mind, and the ideas of the ideas of the
modifications of the human body, in so far as they are related to the
mind alone, as every one may easily see.
All ideas are in God and in so far as they are related to God are true
and adequate. No ideas, therefore, are inadequate or confused unless in
so far as they are related to the individual mind of some person. All
ideas, therefore, both adequate and inadequate, follow by the same
necessity.
_The Origin and Nature of Adequate Ideas_
Let there be something, _A_, which is common to all bodies, and which is
equally in the part of each body and in the whole. I say that _A_ can
only be adequately conceived. For the idea of _A_ will necessarily be
adequate in God, both in so far as He has the idea of the human body and
in so far as He has the idea of its modifications, which involve the
nature of the human body, and partly also the nature of external bodies;
that is to say, this idea will necessarily be adequate in God in so far
as He constitutes the human mind, or in so far as He has ideas which are
in the human mind. The mind, therefore, necessarily perceives _A_
adequately, both in so far as it perceives itself or its own or any
external body; nor can _A_ be conceived in any other manner.
Hence it follows that some ideas or notions exist which are common to
all men, for all bodies agree in some things, which must be adequately,
that is to say, clearly and distinctly, perceived by all.
Hence it follows also that the more things the body has in common with
other bodies, the more things will the mind be adapted to perceive.
Those ideas are also adequate which follow in the mind from ideas which
are adequate in it. For when we say that an idea follows in the human
mind from ideas which are adequate in it, we do but say that in the
divine intellect itself an idea exists of which God is the cause, not in
so far as He is infinite, nor in so far as He is affected by the ideas
of a multitude of individual things, but in so far only as He
constitutes the essence of the human mind.
I have thus explained the origin of those notions which are called
common, and which are the foundations of our reasoning; but of some
axioms or notions other causes exist which it would be advantageous to
explain by our method, for we should thus be able to distinguish those
notions which are more useful than others, and those which are scarcely
of any use; those which are common; those which are clear and distinct
only to those persons who do not suffer from prejudice; and, finally,
those which are ill-founded. Moreover, it would be manifest whence these
notions which are called _second_, and consequently the axioms founded
upon them, have taken their origin, and other things, too, would be
explained which I have thought about at different times. Since, however,
I have set apart this subject for another treatise, and because I do not
wish to create disgust with excessive prolixity, I have determined to
pass by these matters here.
But not to omit anything which is necessary for us to know, I will
briefly give the causes from which terms called _Transcendental_, such
as _Being_, _Thing_, _Something_, have taken their origin. These terms
have arisen because the human body, inasmuch as it is limited, can form
distinctly in itself a certain number only of images at once. If this
number be exceeded, the images will become confused; and if the number
of images which the body is able to form distinctly be greatly exceeded,
they will all run one into another. Since this is so, it is clear that
in proportion to the number of images which can be formed at the same
time in the body will be the number of bodies which the human mind can
imagine at the same time. If the images in the body, therefore, are all
confused, the mind will confusedly imagine all the bodies without
distinguishing the one from the other, and will include them all, as it
were, under one attribute, that of being or thing.
The same confusion may also be caused by lack of uniform force in the
images and from other analogous causes, which there is no need to
discuss here, the consideration of one cause being sufficient for the
purpose we have in view. For it all comes to this, that these terms
signify ideas in the highest degree confused. It is in this way that
those notions have arisen which are called _Universal_, such as, _Man_,
_Horse_, _Dog_, etc.; that is to say, so many images of men, for
instance, are formed in the human body at once, that they exceed the
power of the imagination, not entirely, but to such a degree that the
mind has no power to imagine the determinate number of men and the small
differences of each, such as color and size, etc. It will therefore
distinctly imagine that only in which all of them agree in so far as
the body is affected by them, for by that the body was chiefly affected,
that is to say, by each individual, and this it will express by the name
_man_, covering thereby an infinite number of individuals; to imagine a
determinate number of individuals being out of its power.
But we must observe that these notions are not formed by all persons in
the same way, but that they vary in each case according to the thing by
which the body is more frequently affected, and which the mind more
easily imagines or recollects. For example, those who have more
frequently looked with admiration upon the stature of men, by the name
_man_ will understand an animal of erect stature, while those who have
been in the habit of fixing their thoughts on something else, will form
another common image of men, describing man, for instance, as an animal
capable of laughter, a biped without feathers, a rational animal, and so
on; each person forming universal images of things according to the
temperament of his own body. It is not therefore to be wondered at that
so many controversies have arisen amongst those philosophers who have
endeavored to explain natural objects by the images of things alone.
_The Three Kinds of Knowledge_
From what has been already said, it clearly appears that we perceive
many things and form universal ideas:
1. From individual things, represented by the senses to us in a
mutilated and confused manner, and without order to the intellect. These
perceptions I have therefore been in the habit of calling knowledge
from vague experience.
2. From signs; as, for example, when we hear or read certain words, we
recollect things and form certain ideas of them similar to them, through
which ideas we imagine things. These two ways of looking at things I
shall hereafter call knowledge of the first kind, opinion or
imagination.
3. From our possessing common notions and adequate ideas of the
properties of things. This I shall call reason and knowledge of the
second kind.
Besides these two kinds of knowledge, there is a third, as I shall
hereafter show, which we shall call intuitive science. This kind of
knowing advances from an adequate idea of the formal essence of certain
attributes of God to the adequate knowledge of the essence of things.
All this I will explain by one example. Let there be three numbers given
through which it is required to discover a fourth which shall be to the
third as the second is to the first. A merchant does not hesitate to
multiply the second and third together and divide the product by the
first, either because he has not yet forgotten the things which he heard
without any demonstration from his school-master, or because he has seen
the truth of the rule with the more simple numbers, or because from the
19th Prop. in the 7th book of Euclid he understands the common property
of all proportionals.
But with the simplest numbers there is no need of all this. If the
numbers 1, 2, 3, for instance, be given, every one can see that the
fourth proportional is 6 much more clearly than by any demonstration,
because from the ratio in which we see by one intuition that the first
stands to the second we conclude the fourth.
To knowledge of the first kind we have said that all those ideas belong
which are inadequate and confused, and, therefore, this knowledge alone
is the cause of falsity. Moreover, to knowledge of the second and third
kind we have said that those ideas belong which are adequate, and
therefore this knowledge is necessarily true.
It is the knowledge of the second and third, and not that of the first
kind, which teaches us to distinguish the true from the false. For he
who knows how to distinguish between the true and the false must have an
adequate idea of the true and the false, that is to say, he must know
the true and the false by the second or third kind of knowledge.
_Reason and Imagination_
It is in the nature of reason to perceive things truly, that is to say,
as they are in themselves, that is to say, not as contingent but as
necessary.
Hence it follows that it is through the imagination alone that we look
upon things as contingent both with reference to the past and the
future.
How this happens I will explain in a few words. We have shown above that
unless causes occur preventing the present existence of things, the mind
always imagines them present before it, even if they do not exist.
Again, we have shown that if the human body has once been simultaneously
affected by two external bodies, whenever the mind afterwards imagines
one it will immediately remember the other; that is to say, it will
look upon both as present before it, unless causes occur which prevent
the present existence of the things. No one doubts, too, that we imagine
time because we imagine some bodies to move with a velocity less, or
greater than, or equal to that of others.
Let us therefore suppose a boy who yesterday, for the first time, in the
morning saw Peter, at midday Paul, in the evening Simeon, and to-day in
the morning again sees Peter. It is plain that as soon as he sees the
morning light he will imagine the sun passing through the same part of
the sky as on the day preceding; that is to say, he will imagine the
whole day, and at the same time Peter will be connected in his
imagination with the morning, Paul with midday, and Simeon with the
evening. In the morning, therefore, the existence of Paul and Simeon
will be imagined in relation to future time, while in the evening, if
the boy should see Simeon, he will refer Peter and Paul to the past,
since they will be connected with the past in his imagination. This
process will be constant in proportion to the regularity with which he
sees Peter, Paul, and Simeon in this order. If it should by some means
happen that on some other evening, in the place of Simeon, he should see
James, on the following morning he will connect in his imagination with
the evening at one time Simeon and at another James, but not both
together. For he is supposed to have seen one and then the other in the
evening, but not both together. His imagination will therefore
fluctuate, and he will connect with a future evening first one and then
the other; that is to say, he will consider neither as certain, but both
as a contingency in the future.
This fluctuation of the imagination will take place in the same way if
the imagination is dealing with things which we contemplate in the same
way with reference to past or present time, and consequently we imagine
things related to time past, present, or future as contingent.
_Sub Specie AEternitatis_
It is of the nature of reason to consider things as necessary and not as
contingent. This necessity of things it perceives truly, that is to say,
as it is in itself. But this necessity of things is the necessity itself
of the eternal nature of God. Therefore it is of the nature of reason to
consider things under this form of eternity. Moreover, the foundations
of reason are notions which explain those things which are common to
all, and these things explain the essence of no individual thing, and
must therefore be conceived without any relation to time, but under a
certain form of eternity.
_The Limits of Human Knowledge_
I
The parts composing the human body pertain to the essence of the body
itself only in so far as they communicate their motions to one another
by some certain method, and not in so far as they can be considered as
individuals without relation to the human body. For the parts of the
human body are individuals, composite to a high degree, parts of which
can be separated from the human body and communicate their motions to
other bodies in another way, although the nature and form of the human
body itself is closely preserved. Therefore the idea or knowledge of
each part will be in God in so far as He is considered as affected by
another idea of an individual thing, which individual thing is prior to
the part itself in the order of Nature. The same thing may be said of
each part of the individual itself composing the human body, and
therefore the knowledge of each part composing the human body exists in
God in so far as He is affected by a number of ideas of things, and not
in so far as He has the idea of the human body only; that is to say, the
idea which constitutes the nature of the human mind; and therefore the
human mind does not involve an adequate knowledge of the parts composing
the human body.
We have shown that the idea of a modification of the human body involves
the nature of an external body so far as the external body determines
the human body in some certain manner. But in so far as the external
body is an individual which is not related to the human body, its idea
or knowledge is in God, in so far as He is considered as affected by the
idea of another thing, which idea is prior by nature to the external
body itself. Therefore the adequate knowledge of an external body is not
in God in so far as He has the idea of the modification of the human
body, or, in other words, the idea of the modification of the human body
does not involve an adequate knowledge of an external body.
When the human mind through the ideas of the modifications of its body
contemplates external bodies, we say that it then imagines, nor can the
mind in any other way imagine external bodies as actually existing.
Therefore in so far as the mind imagines external bodies it does not
possess an adequate knowledge of them.
II
The idea of a modification of the human body does not involve an
adequate knowledge of the body itself, or, in other words, does not
adequately express its nature, that is to say, it does not correspond
adequately with the nature of the human mind, and therefore the idea of
this idea does not adequately express the nature of the human mind, nor
involve an adequate knowledge of it.
From this it is evident that the human mind, when it perceives things in
the common order of Nature, has no adequate knowledge of itself nor of
its own body, nor of external bodies, but only a confused and mutilated
knowledge; for the mind does not know itself unless in so far as it
perceives the ideas of the modifications of the body. Moreover, it does
not perceive its body unless through those same ideas of the
modifications by means of which alone it perceives external bodies.
Therefore in so far as it possesses these ideas it possesses an adequate
knowledge neither of itself, nor of its body, nor of external bodies,
but merely a mutilated and confused knowledge.
I say expressly that the mind has no adequate knowledge of itself, nor
of its body, nor of external bodies, but only a confused knowledge, as
often as it perceives things in the common order of Nature, that is to
say, as often as it is determined to the contemplation of this or that
_externally_--namely, by a chance coincidence, and not as often as it is
determined _internally_--for the reason that it contemplates several
things at once, and is determined to understand in what they differ,
agree, or oppose one another; for whenever it is internally disposed in
this or in any other way, it then contemplates things clearly and
distinctly.
III
The duration of our body does not depend upon its essence, nor upon the
absolute nature of God, but the body is determined to existence and
action by causes which also are determined by others to existence and
action in a certain and determinate manner, whilst these, again, are
determined by others, and so on _ad infinitum_. The duration, therefore,
of our body depends upon the common order of Nature and the constitution
of things. But an adequate knowledge of the way in which things are
constituted, exists in God in so far as He possesses the ideas of all
things, and not in so far as He possesses only the idea of the human
body. Therefore the knowledge of the duration of our body is altogether
inadequate in God, in so far as He is only considered as constituting
the nature of the human mind, that is to say, this knowledge in our mind
is altogether inadequate.
Each individual thing, like the human body, must be determined to
existence and action by another individual thing in a certain and
determinate manner, and this again by another, and so on _ad infinitum_.
But we have demonstrated in the preceding proposition, from this common
property of individual things, that we have but a very inadequate
knowledge of the duration of our own body; therefore the same conclusion
is to be drawn about the duration of individual things, that is to say,
that we can have but a very inadequate knowledge of it.
Hence it follows that all individual things are contingent and
corruptible, for we can have no adequate knowledge concerning their
duration and this is what is to be understood by us as their contingency
and capability of corruption; for there is no other contingency but
this.
_The Mind's Knowledge of God_
The idea of an individual thing actually existing necessarily involves
both the essence and existence of the thing itself. But individual
things cannot be conceived without God, and since God is their cause in
so far as He is considered under that attribute of which they are modes,
their ideas must necessarily involve the conception of that attribute,
or, in other words, must involve the eternal and infinite essence of
God.
By existence is to be understood here not duration, that is, existence
considered in the abstract, as if it were a certain kind of quantity,
but I speak of the nature itself of the existence which is assigned to
individual things, because from the eternal necessity of the nature of
God infinite numbers of things follow in infinite ways. I repeat, that I
speak of the existence itself of individual things in so far as they are
in God. For although each individual thing is determined by another
individual thing to existence in a certain way, the force nevertheless
by which each thing perseveres in its existence follows from the eternal
necessity of the nature of God.
The demonstration of the preceding proposition is universal, and whether
a thing be considered as a part or as a whole, its idea, whether it be
of a part or whole, will involve the eternal and infinite essence of
God. Therefore that which gives a knowledge of the eternal and infinite
essence of God is common to all, and is equally in the part and in the
whole. This knowledge therefore will be adequate.
The human mind possesses ideas by which it perceives itself and its own
body, together with external bodies, as actually existing. Therefore it
possesses an adequate knowledge of the eternal and infinite essence of
God.
Hence we see that the infinite essence and the eternity of God are known
to all; and since all things are in God and are conceived through Him,
it follows that we can deduce from this knowledge many things which we
can know adequately, and that we can thus form that third sort of
knowledge. The reason why we do not possess a knowledge of God as
distinct as that which we have of common notions is, that we cannot
imagine God as we can bodies; and because we have attached the name God
to the images of things which we are in the habit of seeing, an error we
can hardly avoid, inasmuch as we are continually affected by external
bodies.
Many errors, of a truth, consist merely in the application of the wrong
names to things. For if a man says that the lines which are drawn from
the center of the circle to the circumference are not equal, he
understands by the circle, at all events for the time, something else
than mathematicians understand by it. So when men make errors in
calculation, the numbers which are in their minds are not those which
are upon the paper. As far as their mind is concerned there is no error,
although it seems as if there were, because we think that the numbers in
their minds are those which are upon the paper. If we did not think so,
we should not believe them to be in error. For example, when I lately
heard a man complaining that his court had flown into one of his
neighbor's fowls, I understood what he meant, and therefore did not
imagine him to be in error. This is the source from which so many
controversies arise--that men either do not properly explain their own
thoughts, or do not properly interpret those of other people; for, in
truth, when they most contradict one another, they either think the same
things or something different, so that those things which they suppose
to be errors and absurdities in another person are not so.
FOOTNOTES:
[18] From the _Improvement of the Understanding_, Sec.Sec. 33-35.