PRINCIPLE OF CONTRADICTION
- the axiom or law of thought that a thing cannot "be and
not be" at the same time, or a thing must either
be or not be,or the same attribute can not at the same time be
affirmed and and denied of the same subject; also called the lawof
the excluded middle.
- contradictory statements cannot both at the
same time be true,
Example:-
- the two propositions "A is B" and "A is not B" are mutually
exclusive.
- Butch is married to Barb but Barb is not married to Butch.----
is an implicit contradiction. It depends on the
unstated but well known principle: if x is married to y, then y is
married to x.
- A love B and A don't love B----is an explicit
contradiction. You can't love someone and not love someone
at the same time.
Application:-
for all propositions p, it is impossible for both
p and not p to be true, or symbolically
∼(p · ∼p),
in which ∼ means “not” and · means “and”