> Is it safe to assume, however, that the contrapositives are true? Couldn't it be possible that there's a situation where they aren't?
>
> -eric "If I'm making an idiotic mathematical error by saying that, forgive me." sleator
> Fri 15 Jun A.D. 2001

The contrapositive of a statement is always a logical equivalent (one is true if and only if the other is true). Maybe you're thinking of the term converse (or inverse)?

If you have the statement "A implies B", the converse is "B implies A", the inverse is "(Not A) implies (not B)", and the contrapositive is "(Not B) implies (not A)". The converse and inverse form another logically equivalent pair (since the inverse is the contrapositive of the converse), but neither are equivalent to the original statement.

--gremlinn