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.