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.
There are many possible counterexamples to the arguments that are invalid; you don’t have to have the counterexamples I provide to be correct.
1. Invalid. Counterexample: Katie is severely mentally handicapped and so is not smarter than a chimpanzee.
2. Invalid. Counterexample: suppose Bob just became a fireman, so he has never actually put out any fires.
3. Invalid. Counterexample: Although Gerald probably knows how to teach mathematics, suppose he has just had a traumatic brain injury and no longer knows how to teach mathematics. And suppose the injury is recent enough for him not to have lost his job as a mathematics professor yet.
4. Invalid. Counterexample: A similar counterexample as #3 would work equally as well here.
5. Valid.
6. Invalid. Counterexample: Perhaps Craig and Linda are married, but Monique is Linda’s secret lover and Craig just finds about it and is angry and hates Monique (but still loves Linda).
7. Invalid. Counterexample: suppose that although Orel Hershizer believes that God exists, in fact God doesn’t exist. In that case, Orel can’t communicate with God, since you can’t communicate with something that doesn’t exist (i.e., communication is a two-way interaction).
8. Valid.
9. Valid.
10.Valid.
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