Cartesian Composites

Towards the end of a paper in which I argued that Descartes thinks a human being is a genuine unity, I invited other commentators to come to Descartes’s defense by accounting for his apparently contradictory claims that a human being is an ens per se and that it is an ens per accidens.¹ These claims seem to be contradictory, because in saying that a human being is an ens per se, Descartes appears to be asserting that a human being is genuinely one, and in saying that a human being is an ens per accidens, he appears to assert that a human being is not genuinely one, but instead is a mere heap or aggregate. In the ensuing eleven years no one has taken up my invitation, except to argue that I was mistaken in claiming that Descartes thinks a human being has per se unity in any robust sense.²

In this paper I will take up the challenge myself, having noticed a similarity between Descartes’s account of the unity of composite substances and his account of composite figures having true and immutable natures. After showing how he can consistently maintain that a human being is both an ens per se and ens per accidens in roughly the same way he can consistently maintain that composite figures both do and do not have true and immutable natures, I will try to respond to criticisms of my claim that he thinks of a human being as a substance or an ens per se.

Let me begin with an analysis and comparison of two passages from the Objections and Replies. In the first, from the Replies to the First Objections, Descartes discusses composite figures. In the second, from the Replies to the Fourth Objections, Descartes discusses composite substances.

Next, to remove the other part of the difficulty, it should be noted that those ideas which do not contain true and immutable natures, but contain only ones which are fictitious and composed by the intellect, can be divided by the same intellect, not only through abstraction, but through a clear and distinct operation, so that any ideas which the intellect cannot so divide were undoubtedly not composed by it. As, for example, when I think of a winged horse, or an actually existing lion, or a triangle inscribed in a square, I easily understand that I can also in opposition think of a horse without wings, a non-existing lion, a triangle without a square, and so on; from which it follows that these do not have true and immutable natures. But if I think of a triangle or a square (I do not speak here of a lion or horse because their natures are not clearly evident to us), then certainly whatever I apprehend as contained in the idea of a triangle, as that its three angles are equal to two right angles, etc., I will truly affirm of the triangle, and of the square whatever is found in the idea of the square. For even if I can understand a triangle, abstracting from the fact that its angles should equal two right angles, I cannot nevertheless deny that of it by a clear and distinct operation, that is, correctly understanding this is what I say. Furthermore, if I consider a triangle inscribed in a square, not in order to attribute to the square those things which pertain only to the triangle or to the triangle those things which pertain to the square, but in order to examine only those things which arise from the conjunction of the two, then its nature will be no less true and immutable than the square or triangle alone, and it will be permitted to affirm that the square is not less than twice the triangle inscribed in it and similar things which pertain to the nature of this composite figure. (AT VII 117–8; CSM II 83–4)³

I am not unaware that some substances are commonly called ‘incomplete.’ But if they are said to be incomplete because they cannot exist per se alone, I confess that it seems contradictory to me that...