Full Idea
If causal relations boil down to nothing more than regularities (as Hume suggests), then it is a mistake to regard the absence of a mechanism or causal link between mental events and material events as a special problem.
Gist of Idea
If causation is just regularities in events, the interaction of mind and body is not a special problem
Source
John Heil (Philosophy of Mind [1998], Ch.2)
Book Reference
Heil,John: 'Philosophy of Mind' [Routledge 1998], p.30
A Reaction
So critics of Descartes who were baffled by interaction, were actually sniffing Hume's wholesale scepticism about necessary causation. Even so, physical conjunction is more tangible than spiritual conjunction.