Posted: May 18, 2012 6:19 am
by Thommo
amkerman wrote:Just to be clear, you are still standing by your assertion that,

"If God exists, he is a non-existent"

is a valid premise?

No, I haven't asserted it is. Validity of premises is a different (and much less commonly referred to) thing to validity of arguments.

A valid argument is one in which the logical form is such that each step in the argument is a correct application of a rule of inference (e.g. modus ponens, modus tollens). A valid premise is a premise which is true under all interpretations (which are broadly speaking assignments of truth values to all the propositional variables, at least in propositional logic which is the easiest situation to understand).

An argument can be valid whether or not its premises are true (or valid). An argument is only sound if it is valid and has true premises. You have extensively critiqued arguments as invalid, not unsound.

Given your misunderstanding it's hard to answer your question, because you almost certainly don't mean to ask me if the premise is valid, maybe you want to know if I think it can be adequately represented by a wff (well formed formula) and thus be suitable for use in logical argument, the answer to that is most certainly.