The Logic Forum Discussion Area

Logic
This Forum is Locked
Author
Comment
validity of arguments

q
p --> q
----------
p

-q
p v q
------
p


Are these arguments valid?

Re: validity of arguments

The first argument:

p implies q / q / therefore p

is invalid - this is the fallacy of affirming the antecedent. "p implies q" does not imply "q implies p".

The second argument:

p or q / not-q / therefore p

is valid, provided the "or" is understood as inclusive disjunction. Since at least one of the two theses p,q must be true - then, if one is false, the other must be true.