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An Introduction to Logic

Posted Jan 21, '12 at 2:34pm

Moegreche

Moegreche

3,317 posts

Moderator

Is this argument valid?

Spongebob lives under the sea
There is only one Spongebob
Therefore, there are no Spongebobs who live above sea level


You would need the additional premise that nothing that lives under the sea also lives above sea level, but yeah, it's valid. Although you would need to use Predicate Logic to show its validity.
 

Posted Jan 21, '12 at 3:19pm

soccerdude2

soccerdude2

1,718 posts

Ah yes, because Spongebob might have a second home above sea level

Predicate Logic? Sorry I looked though again and couldn't find it but I might not have looked hard enough

 

Posted Jan 21, '12 at 4:28pm

Moegreche

Moegreche

3,317 posts

Moderator

The logic introduced in this thread is Propositional Logic. Predicate Logic is sort of the next step, like learning arithmetic and then learning algebra. Sometimes it's just called Symbolic Logic, but that's a bit misleading.
Unfortunately, I don't have the time or resources to do a Predicate Logic introduction. It's doubly challenging because Predicate Logic uses symbols that aren't supported by this site. The two main ones are the existential quantifier (which looks like a backward 'E') and the universal quantifier (which looks like an upside-down 'A'). I'm sure that there are plenty of websites out there that have information on this more advanced, and much more powerful logical system.

 

Posted Jan 22, '12 at 4:17pm

Santi_

Santi_

2,418 posts

Well, we're basing our logic on logic we Think we know is true.

 

Posted Jan 22, '12 at 10:52pm

nichodemus

nichodemus

13,580 posts

Knight

we Think we know is true.


Heh. Solipsism for the win.
 

Posted Jan 27, '12 at 7:41pm

Santi_

Santi_

2,418 posts

Yeah, I'm not solipsitic, or whatever you call it. I'm just reasonable, there is a Huge difference.

 

Posted Jan 30, '12 at 9:09am

Moegreche

Moegreche

3,317 posts

Moderator

Denying the truth of logic is not reasonable - it's irrational. Even if solipsism were true, the laws of logic would still hold. Every logical system contains axioms which are *necessarily* true.
But this thread isn't really the place to debate logic itself. That's why I called it 'An Introduction to Logic' and not 'Post Your Idiotic Ideas About Logic Here'.

 

Posted Jan 30, '12 at 9:14am

nichodemus

nichodemus

13,580 posts

Knight

Santi, that statement is solipsistic if I'm not wrong. Solipsism as an epistemological position holds that knowledge of anything outside one's own mind is unsure.

Either way, I would just doubt you, since I've seen you tell people that you twist the concept of logic, wrap it up in nice sentences and toss it at us whilst not even knowing what it means.

 

Posted Jan 30, '12 at 9:20am

Devoidless

Devoidless

3,838 posts

But this thread isn't really the place to debate logic itself. That's why I called it 'An Introduction to Logic' and not 'Post Your Idiotic Ideas About Logic Here'.


You heard the man.
 

Posted Mar 1, '12 at 7:38pm

Santi_

Santi_

2,418 posts

Listen, I didn't mean to do anything, I'll just butt out. That was a while ago, when I was still pretty new to here, but sorry.

 
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