On 10/19/2013 12:23 PM, 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 > > where it's impossible to know the truth value of H given all available > definitions, permissible reasoning methods within the underlying logic > framework [FOL(=) in this case.] >
And, the meaning of "impossible to know"?
Please go look at some web pages on epistemic logic and modal logic.
In addition, using the same conditional for this statement and for the classical material conditional is confusing. In your use here, you admit a truth value called "maybe" for H against which you claim that the truth value of C is indeterminate.
That is not how the material conditional is interpreted. H can only be taken as true or false -- even if that relegates its use to a hypothetical, perfect knowledge.