Many philosophers accept some version of a principle that says for all x, if x exists, then x plays a unique causal role. After briefly clarifying one version of the principle in Section 1, Section 2 gives reasons to doubt it by showing that there are non-identical 'causal indiscernibles'--I call them 'married causes.' Section 3 then sketches a few philosophical puzzles for which married causes may be helpful.
Engelhardt, Jeff, "Married Causes" (2014). Dickinson College Faculty Publications. Paper 76.