Determinism

[Caecilian]

To reiterate, there is only one possible future if:

1. Causal determinism is true

and

2. The many worlds interpretation of QM is false.

How do you exclude that there might be other descriptions of reality than Many Worlds that allow co-existence of causal determinism and multiple futures?

Good point. I'll amend that to:

2. Deterministic microphysical descriptions of reality which allow for multiple futures (such as the many worlds interpretation of QM) are false.

The point I was making is not about these descriptions being absolute true descriptions of reality but about logical neccessity: Many Worlds shows that there is no logical neccesity that fully deterministic descriptions imply one possible future. In other words, the very definition of determinism should not be overstated in that way.

Sure, your point about no logical necessity is very similar to my point about determinism and 'one possible future' being separable.