Full Idea
When two processes intersect, and they undergo correlated modifications which persist after the intersection, I shall say that the intersection is a causal interaction. I take this as a fundamental causal concept.
Gist of Idea
A causal interaction is when two processes intersect, and correlated modifications persist afterwards
Source
Wesley Salmon (Causality: Production and Propagation [1980], §4)
Book Reference
'Causation', ed/tr. Sosa,E. /Tooley,M. [OUP 1993], p.164
A Reaction
There may be a problem individuating processes, just as there is for events. I like this approach to causation, which is ontologically sparse, and fits in with the scientific worldview. Change of properties sounds precise, but isn't. Stick to processes.