If–Then

Implication and its traps

An interactive lesson with 6 steps, about 5 minutes: you predict, drag and solve, with instant feedback on every answer. It runs in your browser and needs JavaScript.

What you’ll learn

• $P \Rightarrow Q$ is false only when P is true and Q is false.
• The contrapositive is equivalent to the original. The converse is not.
• When testing a rule, look for cases that could break it.

Steps

1. The four cards
2. Implication
3. Equivalent?
4. Necessary or sufficient?
5. Affirming the consequent
6. A vacuous truth