Full Idea
In causation there is 'overdetermination' (c and d occurred, and were both sufficient for e), 'pre-emption' (c and d occurred, and d would have stepped in if c hadn't), or 'fail-safe' (if c hadn't occurred, d would have occurred and done it).
Gist of Idea
Causal overdetermination is either actual overdetermination, or pre-emption, or the fail-safe case
Source
E.J. Lowe (A Survey of Metaphysics [2002], p.179)
Book Reference
Lowe,E.J.: 'A Survey of Metaphysics' [OUP 2002], p.179
A Reaction
Two safety nets together, two safety nets spaced apart, or a second net which pops in if the first breaks. Nice distinctions.