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Is all logic/reasoning circular?

  1. Apr 9, 2007 #1
    Is all logic/reasoning circular?

    Consider this: Science uses experimentation and physical evidence (logic, reasoning, and the senses) to prove or disprove a hypothesis, theory, or judgment. The hypothesis/theory/judgment, however, was made by using logic/reasoning/senses.

    We essentially "created" human logic and reasoning. By using logic and reasoning to prove theories that were created by our own logic and reasoning, are we really proving anything at all?
     
  2. jcsd
  3. Apr 9, 2007 #2
    Let's take mathematics, which doesn't depend on external reality (though it can be guided by needs in physics).

    There's no possible algorithm given a list of axioms that generates all possible proofs or proves the truth or falsity of all possible statements in that axiomatic set.

    The discovery of proofs therefore adds fundamentally new information to our system of knowledge. Without proof, we would have no way of knowing whether (e.g.) the Pythagorean theorem were true no matter how many triangles we tested.

    Even 'experimental mathematics' in which we use computers to find results we couldn't feasibly do by hand adds evidence that was not previously available to us.

    I'm sure others will chirp in with better examples.
     
  4. Apr 10, 2007 #3
    If it turned out that logic was circular, would you stop using it?

    If you answered yes, then please explain why. See if your reason stands up to public scrutiny.

    If you answered no, then think about what that means. Even if you can't ground your use of logic in some stable, proven set of matter of fact claims, and you're still compelled to use it. That should give you a hint as to how logic is grounded.

    Edit: I actually see a thread that's really, really similar on this page. Perhaps reading what's there may help.

    https://www.physicsforums.com/showthread.php?t=154450
     
    Last edited: Apr 10, 2007
  5. Apr 10, 2007 #4
    How would you go about proving that all logic/reasoning is circular without committing the fallacy of circular logic?


    Bar axioms, logic/reasoning is not circular.
     
  6. Apr 10, 2007 #5
    I would probably still use logic but only because we have seen how it is useful for us. It's practical. I'm not sure if that actually answers the question though.

    Maybe I'm not explaining myself correctly: Continuing with mathematics for example. I create a system of numbers and say that I have 2 apples. From that point on everyone says and believes that I have 2 apples. Do I really have 2 apples? Or is it just that I have defined my set of fruit as being 2 apples and in reality this statement means nothing because I could be holding any amount of anything?
     
  7. Apr 10, 2007 #6

    Hurkyl

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    Does it matter? A rose by any other name would smell as sweet.
     
  8. Apr 10, 2007 #7
    You could define the dollar in your pocket as 'a million bucks' too. However, try buying a car with redefined currency and you'll find that you won't get too far.
     
  9. Apr 10, 2007 #8
    :rofl: And that's exactly why I said I would still use logic because it is practical. The entire way we live is made off of this system. But can we really say anything about "reality" or that something is a "fact." Do we really "know" anything?

    Maybe I am asking about truth. Can we really find truth using the system of logic we have created?

    Hurkyl:

    It only smells sweet because that's the word we decided to use to describe the smell.
     
  10. Apr 10, 2007 #9

    Hurkyl

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    Of course -- because we decided to use the word "truth" to describe what we can find with logic. :wink:
     
  11. Apr 10, 2007 #10
    Your right. What is it that we find with logic though?
     
  12. Apr 10, 2007 #11
    this is not true
     
  13. Apr 10, 2007 #12
    Why isn't it true?
     
  14. Apr 12, 2007 #13
    It doesn't seem true to say that we created it.

    It really seems as though we're just formalizing what was already there in our language. Or better yet, formalizing certain thought processes in people.

    Even Aristotle agreed that you couldn't "prove" certain fundamental ideas in logic like the principle of non-contradiction. What he did do was give arguments which show everyone is committed to using the principle of non-contradiction.

    I like the wikipedia article here
    http://en.wikipedia.org/wiki/Principle_of_non-contradiction

    Certainly an important principle like non-contradiction is undeniable, but is it demonstrable? If it isn't demonstrable, then how can you say we created it?

    I think we preserve it with our systems of logic. Logic doesn't actually tell me much about the world (physics and chem help more with that), so how am I supposed to find truth with logic?
     
    Last edited: Apr 12, 2007
  15. Apr 16, 2007 #14
    I suppose you are right about not creating it.

    Physics and Chem (along with all science) uses logic/reason. If Physics tells about the world then so does the use of logic/reason.
     
  16. Apr 19, 2007 #15
    Because abstract concepts aren't "created". For X to be created by Y, Y needs to be the cause of X existence. This is not true about logic and humans.
     
    Last edited: Apr 19, 2007
  17. Apr 19, 2007 #16
    The word "created" is commonly applied to material things instead of mental constructs. A better word may be "formulated" with regards to the latter.

    Can we not say that logic was formulated by humans? Since it takes mental abilities to formulate abstract concepts, the conclusion seems to be that logic as we know it was formulated by humans.
     
  18. Apr 19, 2007 #17
    He used the word "made", so it's pretty clear he doesn't mean "formulated". Also if you substitute "formulated" for "made" in the original statement it becomes non sequitur.
     
  19. Apr 19, 2007 #18
    I don't think it's all that clear so we should ask. GTdan?

    My take: since as you said you cannot really "make" an abstract concept, yet we use it, then it must exist in some form. I assume we formulate it because I don't know how logic can be used without being formulated.

    Replacing terms, the statement summarizes into something like this:

    Given this point of view, the answer to "Is all logic/reasoning circular?" would be yes.
     
  20. Apr 20, 2007 #19
    I think the word formulated falls in line better with what I was thinking at the time. Note in my first post I put quotations around the word, create.

    After JonF and AsianSensationK explained that you can't really create logic, I was kind of left at odds on how to explain what I was trying to say. So yeah, "formulated" definitely fits the bill.
     
    Last edited: Apr 20, 2007
  21. Apr 20, 2007 #20
    Yes. If you mean we the way we've formulated logic makes it circular, then it seems that you're right.

    Even if we didn't create some of the fundamental ideas of logic, we certainly have to try and justify our definitions to ourselves, and the only way we can do that is by appealing to and utilizing the ideas we're trying to describe.
     
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