Full Idea
It would seem that whatever exists at any part of time has causal relations. This is not a distinguishing characteristic of what exists, since we have seen that two non-existent terms may be cause and effect.
Gist of Idea
What exists has causal relations, but non-existent things may also have them
Source
Bertrand Russell (The Principles of Mathematics [1903], §449)
Book Reference
Russell,Bertrand: 'Principles of Mathematics' [Routledge 1992], p.476
A Reaction
Presumably he means that the non-existence of something (such as a safety rail) might the cause of an event. This is a problem for Alexander's Principle, in Idea 3534. I think we could redescribe his problem cases, to save Alexander.
Related Idea
Idea 3534 To be is to have causal powers [Alexander,S]