Formal Fallacies : Which of the following arguments are valid and which are inva

Question

Formal Fallacies: Which of the following arguments are valid and which are invalid?

1. Jan is a woman if Jan is a person. Jan is a person, so Jan is a woman.

2.Ken is not both a fisherman and a pilot. Therefore, either Ken is not a fisherman or Ken is not a pilot.

3.Jan is a woman if Jan is a person. Jan is not a person, so Jan is not a woman.

4.Jason is both not a lawyer and not a doctor. Consequently, Jason is neither a lawyer nor a doctor.

5.Either you are bored or happy. You are unhappy, so you are bored.

6. If David is rich, then he is famous. David is not famous. Hence, he is not rich.

7.Ken is not both a fisherman and a pilot, so Ken is both not a fisherman and not a pilot.

8.If you study, you will pass. Consequently, if you do not study, you will not pass.

9.Either you passed the exam or you are unhappy. You are unhappy. Consequently, you did not pass the exam.

10. Dan is a man only if Dan is a person. Dan is a person. Thus, Dan is a man.

11.Either Jill is not a Democrat or Jill is not a Republican. Thus, Jill is neither a Democrat nor a Republican.

12.If Meggan is graduating, then she has completed all of her requirements. Hence, if Meggan has not completed all of her requirements, then she is not graduating.

Explanation / Answer

1. Valid

As Jan is a person, so Jan is a woman.

2. Valid

Ken is not both a fisherman and a pilot.

=>Ken is either a fisherman or a pilot.

Therefore, either Ken is not a fisherman or Ken is not a pilot.

3. Valid

3.Jan is a woman if Jan is a person.

=> Jan is not a person, so Jan is not a woman.

4. Valid

Jason is both not a lawyer and not a doctor.

=> Jason is neither a lawyer nor a doctor.

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