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