Although it may exaggerate to say that Descartes fathered the mechanization of biology, it is true (without qualification) that his Treatise of Man provided the first systematic development of the idea that a complete understanding of all the phenomena of life, including all abilities and behaviour of (non-human) animals, can be achieved by viewing living things as machines. To make this out, Decartes had to learn to think about living things in a new way. My first aim here is to identify the fundamental conceptual innovations at work in Descartes’ attempt to extend the new mechanics to include biology. My second aim is to locate the point at which Descartes’ mechanical imagination runs out. This requires study of Descartes’ scientific work on sense.

The influence of St. Ignatius of Loyola's Spiritual Exercises on Descartes’ work, including the Meditations, has been recognized and discussed by many historians. I just mention a few fairly recent and easily accessible instances. In The Metaphysics of Descartes (Oxford: Clarendon 1965), J. L. Beck suggests that the literary form of the Meditations is most likely due to the Ignatian meditations to which Descartes had been exposed during his training at the Jesuit college of LaFlèche (31). Arthur Thomson in ‘Ignace de Loyola et Descartes’ traces some elements in Descartes’ method and psychology to Ignatian sources, mainly focusing on the Discourse.

Suppose that in the Meditations Descartes thinks he needs to prove that his clear and distinct perceptions are true. There can be little doubt that if he does think he needs to do this, he thinks that the way to do it is to prove that ‘a non-deceiving God exists’ is true. Now suppose that Descartes does come up with such a proof. Presumably he clearly and distinctly perceives both the premisses and that ‘a non-deceiving God exists’ follows from them. But that will not suffice to prove that ‘a non-deceiving God exists’ is true. For, if there is a problem about whether clear and distinct perceptions are true, then in advance of settling it, there is a problem about whether what is proved merely on the basis of clear and distinct perceptions is true.

Self-deception is commonly viewed as a condition that bespeaks irrationality. This paper challenges that view. I focus specifically on the connection between self-deception and practical reasoning, an area which, despite its importance for understanding self-deception, has not been systematically explored. I examine both how self-deception influences practical reasoning and how this influence affects the rationality of actions produced by practical reasoning. But what is self-deception? There are many accounts, yet there is probably none sufficiently well known and compelling to serve as an adequate background given my purposes. Hence, I shall briefly present my own account of self-deception and, on that basis, explore its connections with practical reasoning and rational action.