  First, Reid is committed to the positive role of mathematics in stating and testing theories. Only in that field do we “find no sects, no contrary systems, and hardly any disputes” (EIP 6.4, 457). Newton's greatness lies in part due to the fact that he places physics upon firm mathematical ground, in sharp contrast to Cartesian physics, its leading competitor of the time.  Second, Reid says that issues about causation are not issues physics should attempt to resolve. This counterintuitive commitment is explained by the fact that Reid believes causes, when that term is used properly, are efficient causes (The Correspondence of Thomas Reid, abbreviated ‘Correspondence’ below, 2006, 158). Not only this, efficient causes are only ever agents (EAP 1.5, 30–32; for more about this, see 4. Causation and Free Will, below). Reid attributes this position to Newton. Reid mentions on many occasions, and with a certain pride, that Newtonian science does not permit knowledge of causes of phenomena, for example, the motion of the compass needle or the attraction of two bodies. Here and elsewhere Reid frequently speaks with the scientists and uses ‘cause’ in a colloquial way to refer to physical causes; in doing so, he explicitly follows David Hume's lead. More often, however, Reid urges readers to think of scientific explanation in terms of laws, as Newton had done. Laws are true general propositions used to explain appearances (Thomas Reid on the Animate Creation 1996, 187). Physics does not aim to find efficient causes. By dispensing with causes and amplifying the explanatory value and empirical justification of statements of laws, Reid's account is regarded as a forerunner to a deductive-nomological model of explanation.