The idea of each modification of the human body does not involve an adequate knowledge of the human body itself.
Proof .-- Every idea of a modification of the human body involves the nature of the human body, in so far as the human body is regarded as affected in a given manner (II.

xvi.).

But, inasmuch as the human body is an individual which may be affected in many other ways, the idea of the said modification, &c.
Q.E.D.
PROP.XXVIII.

The ideas of the modifications of the human body, in so far as they have reference only to the human mind, are not clear and distinct, but confused.
Proof .-- The ideas of the modifications of the human body involve the nature both of the human body and of external bodies (II.

xvi.); they must involve the nature not only of the human body but also of its parts; for the modifications are modes (Post.