CHAPTER X. The Nature and Extent of Human Knowledge

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 (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 Æternitatis

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

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.

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:

From the Improvement of the Understanding, §§ 33-35.