Earlier this year I shared my semantic argument with Alexander Pruss. In response he suggested an interesting simplified version of it. I find his suggestion both helpful and promising. Here it is:
1. All the pairs of elementary positive predicates that we know to differ intensionally also differ extensionally.
2. So, probably, all elementary positive predicates that differ intensionally also differ extensionally.
3. Suppose F is an elementary positive universal predicate.
4. Then F and "is something" do not differ extensionally.
5. Therefore F and "is something" do not differ intensionally.
6. Thus, necessarily, something is F if and only if it is something.
7. Necessarily, everything is something.
8. So, necessarily, everything is F.