 Hume’s eighth rule is, as Hume himself implies, a refinement of Hume’s fourth rule; it prevents over-zealous causal ascription to an object. (In his explanation of the rule, Hume presupposes the spatial and temporal contiguity requirement of cause and effect, but it is not an essential feature of the rule.) But the first part of it (“an object, which exists for any time in its full perfection without any effect”) appears to target non-Newtonian theological or Spinozistic arguments, so will not be discussed here.