_Definitions_ I. By body, I understand a mode which expresses in a certain and determinate manner the essence of God in so far as He is considered as the thing extended. II. I say that to the essence of anything pertains that, which being given, the thing itself is necessarily posited, and being taken away, the thing is necessarily taken; or, in other words, that, without which the thing can neither be nor be conceived, and which in its turn cannot be nor be conceived without the thing. III. By idea, I understand a conception of the mind which the mind forms because it is a thinking thing. _Explanation._--I use the word conception rather than perception because the name perception seems to indicate that the mind is passive in its relation to the object. But the word conception seems to express the action of the mind. IV. By adequate idea, I understand an idea which, in so far as it is considered in itself, without reference to the object, has all the properties or internal signs (_denominationes intrinsecas_) of a true idea. _Explanation._--I say internal, so as to exclude that which is external, the agreement, namely, of the idea with its object. V. Duration is the indefinite continuation of existence. _Explanation._--I call it indefinite because it cannot be determined by the nature itself of the existing thing nor by the efficient cause, which necessarily posits the existence of the thing but does not take it away. VI. By reality and perfection I understand the same thing. VII. By individual things I understand things which are finite and which have a determinate existence; and if a number of individuals so unite in one action that they are all simultaneously the cause of one effect, I consider them all, so far, as one individual thing. _Axioms_ I. The essence of man does not involve necessary existence; that is to say, the existence as well as the non-existence of this or that man may or may not follow from the order of Nature. II. Man thinks. III. Modes of thought, such as love, desire, or the emotions of the mind, by whatever name they may be called, do not exist, unless in the same individual the idea exist of a thing loved, desired, etc. But the idea may exist although no other mode of thinking exist. IV. We perceive that a certain body is affected in many ways. V. No individual things are felt or perceived by us excepting bodies and modes of thought. _The Mind of God_ Individual thoughts, or this and that thought, are modes which express the nature of God in a certain and determinate manner. God therefore possesses an attribute, the conception of which is involved in all individual thoughts, and through which they are conceived. Thought, therefore, is one of the infinite attributes of God which expresses the eternal and infinite essence of God or, in other words, God is a thinking thing.