Consequences ...

I've been thinking about what follows from 'we can talk'.  Hinge propositions (since their contraries threaten intelligibility) are obvious candidates.

Something I hadn't thought of is this:  we also need honest and competent interlocutors.  Without these, talk is impossible - and so, they must exists.  To wonder whether there are any is to wonder whether it is possible to talk - to ask whether there are any is to ask whether it is possible to ask questions.

And the link to 'madness' is clear hear, as well.