Full Idea
There can be no question of a causal power's acting one way in one world and another way in a different world.
Gist of Idea
Causal powers must necessarily act the way they do
Source
Brian Ellis (Scientific Essentialism [2001], 1.12)
Book Reference
Ellis,Brian: 'Scientific Essentialism' [CUP 2007], p.53
A Reaction
Perhaps the very core idea of scientific essentialism. It doesn't feel quite right that when you ask for the source of this necessity, you are only told that it is necessary for the very identity of a power. The truth is that it is a primitive of nature.