Last one for tonight

rune2402 · 2007-10-30 18:26:23

Just want to see if you get what i get.

Identify the argument as valid or invalid.
The argument has a true conclusion. All dogs have fur. All cats have fur. ______________ A cat is not a dog.

a. Valid
b. Invalid

I think it is valid.

Last edited by rune2402 (2007-10-30 18:28:01)

Identity · 2007-10-30 18:39:52

What's meant to be in the underlined bit?

rune2402 · 2007-10-30 18:44:59

i think it's just one of those typo type things in text books meant to drive the student crazy. I think they meant to write "therefore."

Last edited by rune2402 (2007-10-30 18:45:15)

Identity · 2007-10-30 19:04:44

"This argument has a true conclusion: All dogs have fur. All cats have fur. A cat is not a dog."

That's invalid, because there is nothing in the statements that tell you a cat is not a dog.

rune2402 · 2007-10-30 20:45:20

Dangit! I suspected that, but i answered wrong. Argh! i kinda felt that the premises implied the conclusion, but i know the premises must directly support the conclusion. ahhh! Thanks my friend.

mathsyperson · 2007-10-31 03:10:27

It depends which bit you're talking about. The argument is invalid, but the part that says that the argument has a true conclusion is valid.

It's perfectly true that cats aren't dogs, it's just that the previous statements didn't imply that.
It seems a bit of a strange way to argue though. If anything, a bad logician would read those two and then think that cats are dogs.

Math Is Fun Forum

#1 2007-10-30 18:26:23

Last one for tonight

#2 2007-10-30 18:39:52

Re: Last one for tonight

#3 2007-10-30 18:44:59

Re: Last one for tonight

#4 2007-10-30 19:04:44

Re: Last one for tonight

#5 2007-10-30 20:45:20

Re: Last one for tonight

#6 2007-10-31 03:10:27

Re: Last one for tonight

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