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.