Difference between revisions of "Contrapositive"

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-The '''contrapositive''' of a statement of the form "A implies B" is the [[logic]]ally equivalent statement "not-B implies not-A."
-Do not confuse the '''contrapositive''' with the [[converse]], which is very different and not necessarily true.
-For example, let A be the statement "R is a square" and B be the statement "R is a rectangle".  Then A implies B.  The contrapositive of this is the statement "if R is not a rectangle, then R is not a square", which is logically equivalent to the first statement.  On the other hand, the converse is "if R is a rectangle, then R is a square", an implication which isn't even true!
-[[Category:Logic]]