http://gametheory101.com/courses/logic-101/ This lecture introduces the IF-THEN logical operator, commonly also known as the conditional, material conditional, or implication. If the first half of a conditional is true, then the second half of the conditional must be true as well. Unlike other logical connectors, conditionals appear in English in many different formats. This lecture looks at a few of the more common ones: "only if," "required," "sufficient," and "necessary."