In my last post, I discussed how to evaluate arguments. At the end of that piece I provided some examples of formal and informal arguments. Below is the answer key for those examples.
FORMAL AND INFORMAL ARGUMENT EXAMPLES
Identify which of the following is a formal and which is an informal argument. Can you tell which of the formal arguments are valid and which are invalid?
1. Mary is sulking, and she skipped dinner. I bet she’s depressed again. [Informal]
2. Frogs are amphibians, and amphibians are vertebrates, so frogs are vertebrates. [Formal, valid]
3. All Marxists are socialists, so all socialists are Marxists. [Formal, invalid]
4. The trashcan is turned over, the garbage is everywhere, and I see paw prints. The dog must’ve gotten into the trash. [Informal]
5. If it rains, Ronny takes the bus, and I know he took the bus, so it must be raining. [Formal, invalid]
6. Rex is a dog, and no dogs can solve logic problems, so Rex can’t solve logic problems. [Formal, valid]
7. If it rains, Ronny takes the bus, and it’s not raining, so he must not be taking the bus. [Formal, invalid]
8. ‘Neo’ is the hacker alias of Thomas Anderson, and ‘Neo’ is an anagram of ‘One.’ An anagram is a word that’s produced by rearranging the letters of a different word. [Not an argument!]
9. George can’t be that serious about Sally. If he were, he’d quit messing around with Angela, and I saw the two of them heading into the Motel 6 last night. [Formal, valid]
10. Ethel is a monstrously big woman, and she does have a beard, so she really ought to join the circus. [Informal]
Mark T. Conard 