 For each of these putative causal relations, we can raise metaphysical questions: What are their relata? What is their arity? In virtue of what do those relata stand in the relevant causal relation? And how does this kind of causal relation relate to the others? Of course, there is disagreement about whether each—or any—of these relations exists. Russell (1912: 1) famously denied that there are any causal relations at all, quipping that causation is “a relic of a bygone age, surviving, like the monarchy, only because it is erroneously supposed to do no harm” (see also Norton 2003). Others may deny that there is a relation of general causation or influence at all, contending that claims like 2 and 3 are simply generalizations about token causal relations (see  §2.1  below). There will also be disagreement about whether these relations are reducible, and, if so, what they can be reduced  to—probabilities,  regularities,  counterfactuals,  processes,  dispositions,  mechanisms,  agency,  or what-have-you. This entry will not attempt to survey the range of potential answers to these questions. Instead, it will focus on more general questions about the causal relata, the arity of the causal relation, prominent or controversial instances of these causal relations, how the different relations are themselves related, and so on.