Full Idea
Hume's regularity theory of causation is only a theory about causation so far as we can know about it or contentfully conceive of it in the objects, not about causation as it is in the objects.
Gist of Idea
Hume says we can only know constant conjunctions, not that that's what causation IS
Source
report of David Hume (Enquiry Conc Human Understanding [1748], IV.I) by Galen Strawson - The Secret Connexion App C
Book Reference
Strawson,Galen: 'The Secret Connexion' [OUP 1992], p.276