A rule of
inference in
propositional Logic. Used to break up a
dilemma. It goes like this:
(P>Q) * (R>S)
P^R
Therefore, Q^S.
(Key: >=Implication
*=And
^=Or.)
If it rains, you'll get wet (P>Q). and If it's cold, you'll shiver (R>S).
Either it's raining (P), or it's cold (R).
Therefore, you're either wet, or you're shivering.
(In this case, 'or' is not 'xor', so you might very well be both wet and shivering).
See also: Distructive Dilemma, Disjuctive Sylogism and Modus Ponens.