The notion of metaphysical necessity / possibility

Assignment 5 Instruction
1. Question for The Preliminary Material
The notion of metaphysical necessity / possibility has sometimes been confused with
various epistemic notions. In particular, the notion of being metaphysically necessary has
sometimes been confused with the notion of being knowable a priori. Give examples from
readings and dispel such confusion.

2. Question for Chapter 1 of Forbes 1985
Show that for any frame f (where a frame consists of W and acc) in which the
accessibility relation is symmetric, P ? ? ?P is valid (that is, P ? ? ?P is true on all models
based on f ).
3. Question for Chapter 2 of Forbes 1985
Is (?x)?Fx ? ?(?x) Fx valid in (quantified) S5? If you think so, explain why. If you
think now, give a model to support your view.