There are three basic laws of logic: the law of identity (A=A), the law of non-contradiction (something can't be both true and false at the same time), and the law of excluding middle (something is either true or false, nowhere in-between). I've found many sources that say that these laws are self-evident because if you try to disprove them, you first have to assume they're true. However, non of these sources explain in detail why you have to assume they're true before you try to disprove them. Does anyone have any sources that go into detail on this subject? This is the best I've come up with on my own:

The law of identity states that an object is the same as itself. If you have A, then you have A. The reason this law is self evident is because if someone asks "why is A itself," they must already know what A is. You must already know what A is before you try to prove it's something else, so you must assume that the law of identity is true before you try to disprove it. So trying to disprove this law is self-refuting.


The law of non-contradiction states that something can't be true and false at the same time. A cannot be not A at the same time.  If someone tries to disprove this law, tries to prove that A and not A can exist at the same time, they must first know that A is not not A, so they must assume the law is true before they try to disprove the law. Again, it's self-refuting.


The law of excluding middle states that something is either false or true. Something can't be neither false or true.  If someone tries to prove this law is false, they must already assume that the law can either be true or false. Again, self-refuting.

http://en.wikipedia.org/wiki/Law_of_thought

http://www.debate.org/debates/The-laws-of-logic-are-self-evident./1/

Tags: logic, reasoning, self-evident, truth

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You should read Methods of Logic by Quine if you want to get a little more in-depth. The way you explained it is pretty much spot-on, so I'm not going to really expand on it, because I would likely go on and on about it. Just read Quine. He's much more eloquent than I.

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Posted by Quincy Maxwell on July 20, 2014 at 9:37pm 13 Comments

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