Full Idea
The representation of 'morning star' must be different from 'evening star' because their tokens differ in their causal powers.
Gist of Idea
Co-referring terms differ if they have different causal powers
Source
Jerry A. Fodor (LOT 2 [2008], Ch.3.3)
Book Reference
Fodor,Jerry A.: 'LOT 2: the Language of Thought Revisited' [OUP 2008], p.64
A Reaction
This is Fodor trying to avoid the standard Fregean move of proposing that there are 'senses' as well as references. See Idea 12629. If these two terms have the same extension, they are the same concept? They 'seem' to have two referents.
Related Idea
Idea 12629 For the referential view of thought, the content of a concept is just its reference [Fodor]