Full Idea
There can be constant conjunction without causation (coincidences) and causation without constant conjunction (smoking causes cancer).
Gist of Idea
Coincidence is conjunction without causation; smoking causing cancer is the reverse
Source
S.Mumford/R.Lill Anjum (Getting Causes from Powers [2011], 1.2)
Book Reference
Anjum,R.J./Mumford,S.: 'Getting Causes from Powers' [OUP 2011], p.9
A Reaction
This seems to be presented as a knock-down argument, but I think Humeans can reply to both of them. If you look at the wider pattern of coincidence, or the deeper pattern of coincidence, both of these counterexamples seem to fail.