 there is a striking difference between conjunctive common causes on the one hand and causal processes and interactions on the other. Causal processes and causal interactions seem to be governed by basic laws of nature in ways that do not apply to conjunctive forks. […] Although I am not prepared to argue the case in detail, it seems plausible to suppose that all fundamental physical interactions can be regarded as exemplifications of the interactive fork. Conjunctive common causes are not nearly as closely tied to the laws of nature. […] in contrast to causal processes and causal interactions, conjunctive forks depend crucially on de facto background conditions. (Salmon 1982a [1998: 299])