Full Idea
If a short-circuit causes a fire, the so-called cause is, and is known to be, an Insufficient but Necessary part of a condition which is itself Unnecessary but Sufficient for the result. Let us call this an INUS condition.
Gist of Idea
A cause is an Insufficient but Necessary part of an Unnecessary but Sufficient condition
Source
J.L. Mackie (Causes and Conditions [1965], §1)
Book Reference
'Causation', ed/tr. Sosa,E. /Tooley,M. [OUP 1993], p.34
A Reaction
I'm not clear why it is necessary, given that the fire could have started without the short-circuit. The final situation must certainly be sufficient. If only one situation can cause an effect, then the whole situation is necessary.
Related Idea
Idea 17254 An effect needs a sufficient and necessary cause [Hobbes]