  One important implication of this distinction is that it allows for a fully mechanistic explanation of the physical world. To explain the interaction between two bodies requires alluding only to their physical properties (size, shape and motion) without the need to take recourse to any Aristotelian explanation involving  final causes. Making room for mechanistic explanations, that is, for the New Science, was one of Descartes’ chief motivations for writing the Meditations. Spinoza preserves this aspect of Cartesian doctrine (cf. appendix to Part One of the Ethics and discussion in  Section 1.3.1).