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Contraposition is when we are given a proposition such as "If Socrates is a man then he is a human" and from the given proposition another is inferred having for its subject the contradictory of the original predicate, such as "If Socrates is not a human, then he is not a man."

The contraposition also allows us to negate propositions which may falsely assume to be true or logically sound. Every now and then I also like to attempt to find contrapositions that sound odd or may not fit perfectly to their propositions. It's hard, and I have yet to succeed. But here are some of the closest examples I've come up with, they're not just weak they've all failed at proving anything new in logic...but at least I tried...

If God exists, then he created man.
If he didn't create man, then God doesn't exist.

If man exists, man was created by God
If man wasn't created by God, then man doesn't exist

If a barn exists, then it was built by a farmer
If it wasn't built by a farmer then the barn doesn't exist

If a chicken's egg exists, then it was laid by a chicken
If a chicken's egg wasn't laid by a chicken, then it doesn't exist.

If a pregnant chicken exists, then it lays an egg.
If it doesn't lay an egg, then the pregnant-chicken doesn't exist.

If evolution exists, then it will create man
If it will not create man, then evolution doesn't exist.

If gravity exists, then we can stay on the ground.
If we can't stay on the ground, then gravity doesn't exist.

That's all I have for now, if anyone else came across contrapositions that sound odd, let me know.



If a proposition remains valid in contraposition, then it is valid
If a proposition is not valid, then is will not remain valid in contraposition.

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