Modus Ponens:
	If p, then q.
	p.
	q.
Example:
	If there is no God, then life is meaningless.
	There is no God.
	Life is meaningless.
Modus Tollens:
	If p, then q.
	It is not the case that q.
	It is not the case that p.
Example:
	If an all powerful and all merciful God exists, then there is no evil in the world.
	It is not the case that there is no evil in the world.
	It is not the case that an all powerful and all merciful God exists.