 Finally, there is a fundamental structural similarity between Humean causes and the causes favored by pre-Newtonian Mechanical philosophers (i.e., Boyle, Huygens, etc; for a different argument, see McGuire 1972). They have the same structure: i.e., priority of the cause over the effect, contiguity, and constant conjunction. Now, to be sure, Hume is aware that Newton decisively refuted the Mechanical Philosophy’s program which insisted that explanations be cast in terms of the impact of colliding bodies  (section 4.2).  Hume rejects the ontological and explanatory reductionism of the Mechanical philosophy. Hume introduces eight “rules by which to judge of causes and effects” (see  section 4.5  below) because it is “possible for all objects to become causes or effects to each other” (THN 1.3.15). This is why Hume’s list of “ultimate causes” and “general principles”—“Elasticity, gravity, cohesion of parts, communication of motion by impulse” (EHU 4.1.12)—is more inclusive than the Mechanical philosophy would allow.