Full Idea
There are four causal connections: an event is sufficient for another if it is its cause; an event is necessary for another if it is a condition for it; it is necessitated by another if it is an effect; it is contingent upon another if it is a resultant.
Gist of Idea
Causes are either sufficient, or necessary, or necessitated, or contingent upon
Source
Curt Ducasse (Nature and Observability of Causal Relations [1926], §2)
Book Reference
'Causation', ed/tr. Sosa,E. /Tooley,M. [OUP 1993], p.126
A Reaction
An event could be a condition for another without being necessary. He seems to have missed the indispensable aspect of a necessary condition.