XXIV. The human mind does not involve an adequate knowledge of the parts composing the human body. >>>>>Proof--The parts composing the human body do not belong to the essence of that body, except in so far as they communicate their motions to one another in a certain fixed relation (Def. after Lemma iii.), not in so far as they can be regarded as individuals without relation to the human body. The parts of the human body are highly complex individuals (Post. i.), whose parts (Lemma iv.) can be separated from the human body without in any way destroying the nature and distinctive quality of the latter, and they can communicate their motions (Ax. i., after Lemma iii.) to other bodies in another relation; therefore (II. iii.) the idea or knowledge of each part will be in God, inasmuch (II. ix.) as he is regarded as affected by another idea of a particular thing, which particular thing is prior in the order of nature to the aforesaid part (II. vii.). We may affirm the same thing of each part of each individual composing the human body; therefore, the knowledge of each part composing the human body is in God, in so far as he is affected by very many ideas of things, and not in so far as he has the idea of the human body only, in other words, the idea which constitutes the nature of the human mind (II. xiii.); therefore (II. xi. Cor.), the human mind does not involve an adequate knowledge of the human body. Q.E.D. XXV. The idea of each modification of the human body does not involve an adequate knowledge of the external body. >>>>>Proof--We have shown that the idea of a modification of the human body involves the nature of an external body, in so far as that external body conditions the human body in a given manner. But, in so far as the external body is an individual, which has no reference to the human body, the knowledge or idea thereof is in God (II. ix.), in so far as God is regarded as affected by the idea of a further thing, which (II. vii.) is naturally prior to the said external body. 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. 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 Cor.) it perceives that external body. Q.E.D.