Verifiability ...

After hearing David Chalmers talking about The Matrix in Aberdeen:

This is probably not novel, but the verification theory of meaning had at least one thing to be said for it:  that a statement which cannot in principle be verified or falsified is meaningless.  The difference between the film matrix and the philosophical matrix (the brain in the vat) is that in the film Neo escapes from the matrix.  There is a narrative of discovery.

It's when we think we might live in a matrix from which we cannot escape, that we are thinking nonsense.  We are wondering, then, whether Neo 'really did' escape, or whether he only passed into another illusion - another manifestation of the 'real' matrix.

Without the narrative of escape - the possibility of making a test, at least in principle - the metaphysical speculation becomes meaningless.  With the possibility of a test, the 'metaphysical' speculation stops being metaphysical.  Perhaps we'd better not say it becomes 'scientific', as other tests might be appropriate.

There are some special cases - logical rules, for instance - where the alternative to their truth is that all statements become meaningless.  This prevents certain kinds of (experimental) speculation about alternatives to them, but still allows this argument for their truth to be made.  And in real cases where a potential interlocutor cannot be interpreted in a way which is consistent with their conforming to these rules, exactly their status as an interlocutor is called into question.

When we speak meaningfully, we are not claiming to have a fully worked out verification scheme in mind - far less a methodologically privileged one along the lines of the Logical Positivists' - but we also can't claim that no verification scheme could ever be available.  This claim is catastrophic for meaningfulness.

And, of course, both skeptics and religious believers do make this kind of claim:  the first that nothing can be proved and the others that certain things can never be disproved.