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.