Nam Nguyen wrote: > On 19/10/2013 5:23 AM, Peter Percival wrote: >> Nam Nguyen wrote: >> >>> What definition of "invalidity" were you referring to _here_ ? Mine? >> >> If you use the word "invalidity" is newsgroups called sci.logic and >> sci.math then it should probably be with its usual technical meaning. If >> you use it in another sense you should probably say what sense that is >> right from the start. > > I already did in this very thread define one or two forms of invalidity > for meta statements. If you don't remember then say so and I'll try to > cite the post for you. > > In any rate, one of the forms is that: > > H => C
And is => the truth-functional if-then? If not, what is it?
> where it's impossible to know the truth value of H given all available
And impossibility and knowing are governed by what modal and epistemic logics? If none, how are we to understand "impossible to know"?
> definitions, permissible reasoning methods within the underlying logic > framework [FOL(=) in this case.]
In FOL(=) there are no binary connectives that aren't truth functional, so I'm going to suppose that => is the truth-functional if-then. Nor are there any modal or epistemic operators, so I'm still in the dark regarding "impossible to know".
-- The world will little note, nor long remember what we say here Lincoln at Gettysburg