Validity and Soundness

These sections will introduce you to the concept of validity – the term for when the conclusion of an argument follows from its premises. Pay careful attention to the difference between validity and soundness. All sound arguments are valid, but not all valid arguments are sound. Remember that premises do not have to be true for an argument to be valid.

Complete Exercise 5, checking your answers against the key.

Exercise

Determine whether or not the following arguments are valid by using the informal test of validity. If the argument is invalid, provide a counterexample.

  1. Katie is a human being. Therefore, Katie is smarter than a chimpanzee.
  2. Bob is a fireman. Therefore, Bob has put out fires.
  3. Gerald is a mathematics professor. Therefore, Gerald knows how to teach mathematics.
  4. Monica is a French teacher. Therefore, Monica knows how to teach French.
  5. Bob is taller than Susan. Susan is taller than Frankie. Therefore, Bob is taller than Frankie.
  6. Craig loves Linda. Linda loves Monique. Therefore, Craig loves Monique.
  7. Orel Hershizer is a Christian. Therefore, Orel Hershizer communicates with God.
  8. All Muslims pray to Allah. Muhammad is a Muslim. Therefore, Muhammad prays to Allah.
  9. Some protozoa are predators. No protozoa are animals. Therefore, some predators are not animals.
  10. Charlie only barks when he hears a burglar outside. Charlie is barking. Therefore, there must be a burglar outside.