Full Idea
A cause is an event lasting for a finite time, but if cause and effect are contiguous then the earlier part of a changing cause can be altered without altering the effect, and a static cause will exist placidly for some time and then explode into effect.
Gist of Idea
If causes are contiguous with events, only the last bit is relevant, or the event's timing is baffling
Source
Bertrand Russell (On the Notion of Cause [1912], p.177)
Book Reference
Russell,Bertrand: 'Mysticism and Logic' [Unwin 1989], p.177
A Reaction
[very compressed] He concludes that they can't be contiguous (and eventually rejects cause entirely). This kind of problem is the sort of thing that only bothers philosophers - the question of how anything can happen at all. Why change?