Wherefore an adequate knowledge of the external body is not in God, in so far as he has the idea of the modification of the human body; in other words, the idea of the modification of the human body does not involve an adequate knowledge of the external body.

Q.E.D.
PROP.XXVI.

The human mind does not perceive any external body as actually existing, except through the ideas of the modifications of its own body.
Proof .-- If the human body is in no way affected by a given external body, then (II.

vii.) neither is the idea of the human body, in other words, the human mind, affected in any way by the idea of the existence of the said external body, nor does it in any manner perceive its existence.

But, in so far as the human body is affected in any way by a given external body, thus far (II.xvi.and Coroll.) it perceives that external body.