Inconsistent triad

An inconsistent triad consists of three propositions of which at most two can be true. For example:


 * 1) Alice loves me.
 * 2) If Alice loves me, she would have sent flowers.
 * 3) Alice hasn't sent flowers.

If one finds oneself believing all three propositions of an inconsistent triad, then (to be rational) one must give up or modify at least one of those beliefs. Maybe Alice doesn't love me, or maybe she wouldn't send flowers to me if she did, or maybe she actually has sent flowers.

The problem of evil
The problem of evil is often given in the form of an inconsistent triad. For example, Epicurus gave the following three propositions:


 * 1) Evil and suffering exist in the world.
 * 2) God is all-powerful
 * 3) God is all-loving

Epicurus argued that these propositions were inconsistent, and thus, that there could be no all-powerful, all-loving God.