4.1.4.1. Modus Ponens

Try these first

1. 1.

   What does Modus Ponens state?

   Hint

   Think about conditional statements.

2. 2.

   True or False: Modus Ponens can be used with false antecedents.

   Hint

   What happens if p is false?

3. 3.

   Which of the following is an example of Modus Ponens?

   • If it is sunny
   • then we go outside. It is sunny; therefore we go outside.
   • If p
   • then q. Not p; therefore
   • not q.
   • If p
   • then q. q; therefore
   • p.

   Hint

   Look for the 'if...then' format.

4. 4.

   True or False: The argument form 'If it snows, then roads are slippery. Roads are slippery; thus it must be snowing.' is valid.

   • True
   • False

   Hint

   Consider if it could be slippery for another reason.

5. 5.

   Using the premises: 'If the light is on (p), then the room is bright (q).' and 'The light is on (p)', how would you conclude whether the room is bright (q)?

   Hint

   Check the logical connection between p and q.

6. 6.

   Analyze the statement: 'If you do not eat (p), then you will be hungry (q). You are not hungry (¬q); does it follow that you ate (¬p)? Refute this reasoning.

   Hint

   Think about alternative reasons for ¬q.