Single causes come first...

and general causal laws are derived from them:

"I maintain that the Hume programme has things upside down... Singular causal claims are primary. This is true into senses. First, they are a necessary ingredient in the methods we used to establish generic causal claims. Even the methods that test causal laws by looking for regularities will not work unless some singular causal information is filled in first. Second, the regularities themselves play a secondary role in establishing a causal law. They are just evidence -- and only one kind of evidence is that -- that certain kinds of singular causal fact have happened." -- Nancy Cartwright, Nature's Capacities and Their Measurement, p. 2