In the Third Meditation, Descartes introduces the idea of angel as an instance of an idea the human mind can form from other ideas, namely from the idea of human being and from that of God (AT VII 43, CSM II 29; AT VII 138–39, CSM II 99). In the Conversation with Burman, Descartes reportedly asserts that he cannot say anything about angels’ nature, except that like human minds they are thinking substances (AT V 157–58). However, in discussing Regius's theory that man is a substance by accident (per accidens), Descartes provides one counterfactual detail concerning angelic knowledge. The human mind is really and substantially united to the extension of his body. In consequence of this kind of union, the human mind perceives the mechanical modifications of his body as obscure sensations and passions. By contrast, if an angel were joined to a body, his mind would perceive the modifications of this body as they really are, that is, as the mechanical effects of the external bodies that cause them. Consequently, he would know the former only through clear and distinct ideas (AT III 493, CSMK 206) (see clarity and distinctness). An angel united to a body would realize the kind of union that a pilot bears to his ship, which Descartes opposes to the kind of union that holds in the case of human nature (AT VII 81, CSM II 56). To Burman, Descartes adds that he deems wholly irrelevant what views Aquinas – who had been so concerned with angels to deserve to be called “Doctor Angelicus” – held concerning the nature and mind of angels.

Despite this dismissive attitude, Descartes draws on what Aquinas and John Duns Scotus say about angels in his account of the human mind and the nature of human knowledge. For example, the following Cartesian claims on the angelic mind can be traced directly to Aquinas:

1. 1.The mind directly knows itself; its nature consists in thinking and hence it always thinks (AT III 478, CSMK 203; AT V 193, CSMK 355 (cf. Summa Theologica, I, q.56, a.1; q.58, a.1).

2. 2.Understanding and will, and not imagination and sensation, pertain to the nature of the mind (AT VII 73, CSM II 51) (cf. Summa Theologica I, q.54, a.5).

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