of things: Let another, if he likes, imagine in this piece of wood the Form of fire, the Quality of heat, and the Action which burns it as things altogether diverse; for my part I, who fear I shall go astray if I suppose there to be more in it than I see must needs be there, am content to conceive in it the movement of its parts. (Descartes, quoted in Miles 1988, 100) By thus raising a few simple questions about the example of a piece of wood being burned, Descartes laid open what is perhaps the most important problem with any theory of causation based upon a substance ontology: how can a substantial form be transmitted from a cause to its effect? The rejection of the fourfold causality of Aristotle and the Scholastics by Descartes (and Galilei and Bacon) had a profound influence on subsequent thinkers. Whereas he endorsed matter, and in this particular sense may be said to have subscribed to material causality, he rejected the idea of substantial forms or formal causali-ty. And though he did not deny the existence of final causes - which he identified as God's intentions - he denied the usefulness of such a search. In order to explain nature, we need only examine the efficient causes of things (Descartes [1644] 1983, I: 28). Thus, in effect, there was only one type of cause for Descartes: the efficient cause. However, Descartes endorsed two very different concepts of efficient causality. There are particular