PROP. XXIX. The idea of the idea of each modification of the human body does not involve an adequate knowledge of the human mind.
Proof.—The idea of a modification of the human body (II. xxvii.) does not involve an adequate knowledge of the said body, in other words, does not adequately express its nature; that is (II. xiii.) it does not agree with the nature of the mind adequately; therefore (I. Ax. vi) the idea of this idea does not adequately express the nature of the human mind, or does not involve an adequate knowledge thereof.
Corollary.—Hence it follows that the human mind, when it perceives things after the common order of nature, has not an adequate but only a confused and fragmentary knowledge of itself, of its own body, and of external bodies. For the mind does not know itself, except in so far as it perceives the ideas of the modifications of body (II. xxiii.). It only perceives its own body (II. xix.) through the ideas of the modifications, and only perceives external bodies through the same means; thus, in so far as it has such ideas of modification, it has not an adequate knowledge of itself (II. xxix.), nor of its own body (II. xxvii.), nor of external bodies (II. xxv.), but only a fragmentary and confused knowledge thereof (II. xxviii. and note). Q.E.D.
Note.—I say expressly, that the mind has not an adequate but only a confused knowledge of itself, its own body, and of external bodies, whenever it perceives things after the common order of nature; that is, whenever it is determined from without, namely, by the fortuitous play of circumstance, to regard this or that; not at such times as it is determined from within, that is, by the fact of regarding several things at once, to understand their points of agreement, difference, and contrast. Whenever it is determined in anywise from within, it regards things clearly and distinctly, as I will show below.
PROP. XXX. We can only have a very inadequate knowledge of the duration of our body.
Proof.—The duration of our body does not depend on its essence (II. Ax. i.), nor on the absolute nature of God (I. xxi.). But (I. xxviii.) it is conditioned to exist and operate by causes, which in their turn are conditioned to exist and operate in a fixed and definite relation by other causes, these last again being conditioned by others, and so on to infinity. The duration of our body therefore depends on the common order of nature, or the constitution of things. Now, however a thing may be constituted, the adequate knowledge of that thing is in God, in so far as he has the ideas of all things, and not in so far as he has the idea of the human body only. (II. ix. Coroll.) Wherefore the knowledge of the duration of our body is in God very inadequate, in so far as he is only regarded as constituting the nature of the human mind; that is (II. xi. Coroll.), this knowledge is very inadequate to our mind. Q.E.D.
PROP. XXXI. We can only have a very inadequate knowledge of the duration of particular things external to ourselves.
Proof.—Every particular thing, like the human body, must be conditioned by another particular thing to exist and operate in a fixed and definite relation; this other particular thing must likewise be conditioned by a third, and so on to infinity. (I. xxviii.) As we have shown in the foregoing proposition, from this common property of particular things, we have only a very inadequate knowledge of the duration of our body; we must draw a similar conclusion with regard to the duration of particular things, namely, that we can only have a very inadequate knowledge of the duration thereof. Q.E.D.
Corollary.—Hence it follows that all particular things are contingent and perishable. For we can have no adequate idea of their duration (by the last Prop.), and this is what we must understand by the contingency and perishableness of things. (I. xxxiii., Note i.) For (I. xxix.), except in this sense, nothing is contingent.
PROP. XXXII. All ideas, in so far as they are referred to God, are true.