Neuroscience and free will

If I'm understanding you here, the point is that only mental laws of logic could hold across all possible worlds?

So this is another way of saying that the determination of events has to involve, at some fundamental level, the entities involved in those events to make any possibility determinate?

I still don't understand why a law being necessary means that it holds in all possible worlds, or why it being descriptive means it cannot hold in any possible world. Can't we have one world that is purely deterministic and another world that is deterministic/random and another world that has room for free events?

I'm not great with terminology, but are we ruling out contingent necessity?

~~ Paul