Distinctive definition of 'A Priori' ... tidying up

An 'a priori' statement is one which, though not a logical theorem, cannot be false in any playable language game.  Whether we call logical theora a priori is a matter of taste, but they are certainly not interestingly a priori.

Among necessary falsehoods, we can recognise hypotheses about the impossibility of language in general, claims which are Moorean 'paradoxical' etc.

There is room for us to argue about whether some particular statement is a priori or not - for "Neurath's Boat" type reasons, and because there is an open question bar to a general theory here.  Whether some statements are a priori may be a matter of linguistic experiment - of 'doing philosophy', perhaps.