 On HRT, every effect has a sufficient cause. This does not imply that any event has a sufficient cause, but it says that, if there is a causal relation, it is deterministic. Probabilistic causation is thus not covered by HRT. And while the theory is compatible with a probabilistic analog of causation, we follow Hume in restricting ourselves to deterministic causation in this entry. (See the entry on  probabilistic causation  for an overview of theories of causation, where the underlying processes may be indeterministic.)