Ok, a friend of mine gave me this quote saying that it was a paradox:

"one can't use logic to prove the theory of logic"

I'm wondering, is this quote self-defeating? I'm discussing moral relativism with her(She's a believer.) Any help would be appreciated greatly.



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I once heard Dr. Jason Lisle give an example of someone who denies logic, so a conversation could go something like this:

"Do you believe in the laws of logic?"

"No. Of course not."

"So you DO believe in the laws of logic."


If they say no again, they acknowledge the laws of logic by following their premise, and therefore following logic (to a degree). If they say yes, they're bound to the laws of logic, and their original statement is revoked.

You could also use this asking,

"Are you a moral relativist?"


"So you're NOT a moral relativist."

Hope my 2 cents helps :)

But that's a logical statement. Maybe she uses non-logic to prove the theory of logic.. wait that's not possible. haha

Since any argument requires logic, if one couldn't use logic to argue for logic then there is no way to argue for logic. That is like asking someone to prove that 2+2 equals 4 without using math. Well, the only way to prove a mathematical equation is by using mathematics. 

Some things must be assumed at the outset in order to proceed.  Laws of Logic must be assumed to make any argument for laws of logic, but once they are assumed, you can make a valid argument for it.


I would respond to this person that they are free to disregard the laws of logic, but then they are unable to state anything absolutely, or unable to 'know' anything, since they cannot prove anything without first assuming the laws of logic.


By the way, while we do assume the laws of logic, so we can make an argument for them.  We also have a 'reason' for the laws of logic, and a rational explantion for their existence.  Those without a biblical worldview do not have said rational reason or explanation.

I thought of five ways, so far, to answer this:

  1. Ask her, "Then what do we use?" Any response from her, that is not God (see point 5), has to be outside of logic. Then any response you give can be the opposite of hers, hence her statement becomes false.
  2. The statement uses logic so how does she know her statement is true?
  3. She seems to be saying its circular reasoning if you use logic to prove the theory of logic. But using logic is absolutely unavoidable and it is not necessarily fallacious. Some degree of circular reasoning is unavoidable when proving this. Logic cannot be proved from anything else, otherwise it wouldn’t be logic. Therefore, if it is to be proved, it must use itself as the criterion.
  4. any true presupposition must use itself as part of its own proof
  5. One of God’s many attributes is logic. Since God is ultimate, He can only use Himself as the authority and his authority is revealed to us in the bible.

Hey thanks for the input guys! That will really help. Please please please keep my friend in prayer. :( and pray that I can use the right words in my conversations with her

It's self defeating because you're using the laws of logic to make that sentence itself.

That is basically the equivalent of saying "We cannot use the light of the sun to prove that the sun exists."

Hmmm....Try this next quote: "People can do whatever they want. It's in the constitution"   

Also, I saw this video(it's supposed to be a joke. From how the dark knight rises should have ended, but it shows how moral relativism has limits)


Sorry if a little off topic

Hmmm... That's funny. If the constitution says we can do whatever we want, why are there laws? She's also kind of getting off the topic of morality in my opinion. Doing things, and those things being morally right, are two different concepts. Osama bin Laden certainly wanted to attack America on 9/11. He acted on it, and it killed 3,000+ people. Was that morally right? Of course not. I highly doubt she could ever think murder is morally right, and if there is a moral absolute when it comes to murder, why isn't morality absolute in everything?          

Reminds me of those who say, "THERE ARE NO ABSOLUTES."

To which we respond, "are you absolutely sure of that?"


Jim Brenneman said:

Reminds me of those who say, "THERE ARE NO ABSOLUTES."

To which we respond, "are you absolutely sure of that?"

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