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[sri]

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It pays to discuss argumentation processes using formal techniques of logic and proof principles. For each of the following statements, indicate whether the argument is correct in its deduction, and if not, what exactly is the fallacy. The first one is an example:

1. All fish swim. I swim. Therefore I am a fish.
(Fallacious: All fish may swim; but everything that swims need not be a fish)

2. The truth hurts. If my words hurt you, it is too bad. It just shows that what I said was true.

3. It is a crime to cut someone with a knife. Therefore all surgeons are criminals.

4. The fittest members of any species survive. Those who survive are the fittest.

5. A rich country can afford to build good roads. Building good roads increases economic interactions, making a country rich.

6. Whenever my roommate comes home late and sleeps in his shoes, he wakes up with a headache. Therefore, sleeping with your shoes on causes headache.

7. You are not my friend. Therefore you are my enemy.

[pankaj]

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2.Fallacy: truth may hurt, but it its not true that only truth hurts.

5.Fallacy: To build a good road it needs money, so the one building it must be rich, not going to be rich. (I think !!)

7. Fallacy: There can be other things also than friend and enemy, thats acquainted or unknown, if not friend so its not essentially enemy.

[sids]

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2. The truth hurts. If my words hurt you, it is too bad. It just shows that what I said was true.

Fallacious: Truth may hurt; but truth need not be the only thing that hurts.

3. It is a crime to cut someone with a knife. Therefore all surgeons are criminals.

I think this argument is correct. I don't mean to imply that all surgeons are actually criminals; just that in a universe where the first statement is really true, they are.

4. The fittest members of any species survive. Those who survive are the fittest.

If the second statement was "Those who survive are the fittest members of that species," this would be correct.

5. A rich country can afford to build good roads. Building good roads increases economic interactions, making a country rich.

This seems like some kind of a circular argument. I can clearly see that the argument is fallacious but I am just not able to give words to my thought.

6. Whenever my roommate comes home late and sleeps in his shoes, he wakes up with a headache. Therefore, sleeping with your shoes on causes headache.

Incorrect: here an auxiliary effect is being mis-interpreted as the cause.

7. You are not my friend. Therefore you are my enemy.

This would be true if "friend" and "enemy" were the only possible states. Since that isn't so, this argument is fallacious.

[sri]

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3. It is a crime to cut someone with a knife. Therefore all surgeons are criminals.

I think this argument is correct. I don't mean to imply that all surgeons are actually criminals; just that in a universe where the first statement is really true, they are.

He he 

I wonder what a surgeon has to say to that. I'll give the reasons for the fallacies in a later post after waiting for some more responses.

[sanket]

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4. The fittest members of any species survive. Those who survive are the fittest.

The first sentence does not speak about the survival of the less fit members. It does not say *only* the fittest members survive. Therefore, the second sentence does not follow from the first.

5. A rich country can afford to build good roads. Building good roads increases economic interactions, making a country rich.

Actually, I don't find this wrong. (I know it can be seen as circular, but I feel the "fallacy" hasn't come out "clearly" in the argument.  )

6. Whenever my roommate comes home late and sleeps in his shoes, he wakes up with a headache. Therefore, sleeping with your shoes on causes headache.

This is the common 'correlation implies causation' fallacy. It's true that having a headache and sleeping with shoes on have occurred together. But that need not mean sleeping with shoes on is the cause for the headache.