Part 2: Common ideas

Proposition 31: 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. Corollary: Hence it follows that all particular things are contingent and perishable. Proposition 32: All ideas, in so far as they are referred to God, are true. Proof: All ideas which are in God agree in every respect with their objects (2.7. Coroll.), therefore (1. Ax. 6) they are all true. Q.E.D. Proposition 33: There is nothing positive in ideas, which causes them to be called false. Proof: If this be denied, conceive, if possible, a positive mode of thinking, which should constitute the distinctive quality of falsehood. Proposition 34: Every idea, which in us is absolute or adequate and perfect, is true. Proof: When we say that an idea in us is adequate and perfect, we say, in other words (2.11. Coroll.). Proposition 35: Falsity consists in the privation of knowledge, which inadequate, fragmentary, or confused ideas involve. Proof: There is nothing positive in ideas, which causes them to be called false (2.33). Note: In the note to 2.17, I explained how error consists in the privation of knowledge, but in order to throw more light on the subject I will give an example.   Proposition 36: Inadequate and confused ideas follow by the same necessity, as adequate or clear and distinct ideas. Proof: All ideas are in God (1.15), and in so far as they are referred to God are true (2.32) and (2.7. Coroll.) adequate.   Proposition 37: That which is common to all (cf. Lemma 2, above), and which is equally in a part and in the whole, does not constitute the essence of any particular thing. Proof: If this be denied, conceive, if possible, that it constitutes the essence of some particular thing.   Proposition 38: Those things, which are common to all, and which are equally in a part and in the whole, cannot be conceived except adequately. Proof: Let A be something, which is common to all bodies, and which is equally present in the part of any given body and in the whole. Corollary: It follows that there are certain ideas or notions common to all men.   Proposition 39: That, which is common to and a property of the human body and such other bodies as are wont to affect the human body, and which is present equally in each part of either, or in the whole, will be represented by an adequate idea in the mind. Proof: If A be that, which is common to and a property of the human body and external bodies, and equally present in the human body and in the said external bodies, in each part of each external body and in the whole, there will be an adequate idea of A in God (2.7. Coroll.), both in so far as he has the idea of the human body, and in so far as he has the ideas of the given external bodies. Corollary: Hence it follows that the mind is fitted to perceive adequately more things, in proportion as its body has more in common with other bodies.