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Question about logic.

  1. Oct 8, 2011 #1
    I will try to make my OP based on the rules this sub-forum subscribes to, if not please inform me. Sorry.

    My question is about logic. How did we acquire it? Was it evolutionary? How is it that Japanese logicians do very much the same work as white American ones do. I am asking because logic seems so fundamental to everything we do.

  2. jcsd
  3. Oct 8, 2011 #2
    There is no single type of logic proven to describe everything we observe and the brain is still a huge mystery in many respects so this question prompts endless metaphysical speculation. However, I would suggest that looking for patterns in the world around us promotes survival and it is pretty obvious evolution selects for the ability to use logic.
  4. Oct 10, 2011 #3


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    Perhaps it's worthwhile to define logic more broadly (as it is commonly used) as ANY formal system of thought; any system of reasoning which follows a consistent set of rules.

    Therefore, you can say that someone has poor logic (a system of reasoning that yields incorrect results) or someone is being illogical (making decisions that would seem to defy a formal system of thought).

    So, how did we acquire it? Through judicious application and refinement. The universe seems to be imbued with a sort of implicit logic which can be discovered and mankind seems to be able to formulate its own system of logic which can take known truths and help to reveal new truths.
  5. Oct 30, 2011 #4
    Don't forget about the difference between Sophism, to use clever deceit, and Paralogism, an argument violating the principles of valid reasoning.
  6. Nov 11, 2011 #5
    Logic is abstraction of the world surrounding us. Or more precisely, it is abstraction of our perception of the world. Just like math. It is not fundamental at all. Only your perception makes you feel it is fundamental.

    It is quite possible that some life can exist who can perceive directly the quantum weirdness. They probably would have similar feeling that randomness is fundamental.
  7. Nov 11, 2011 #6


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    But only valid, working logic can carry you from initial known truths to new, previously unknown, truths.

  8. Nov 11, 2011 #7
    Please, give an example of that happening.

    This question does not give any clue what is your problem with understanding what I've said.
  9. Nov 11, 2011 #8


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    I don't understand why you speculated about a lifeform that could experience, first hand, "quantum weirdness." The topic is logic.

    You're talking about intuition. The workings of the universe on very small scales are non-intuitive, they're not illogical. I don't even know what it would mean for physics to be illogical. Furthermore, the antithesis of logic would not be randomness.
  10. Nov 11, 2011 #9


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  11. Nov 11, 2011 #10


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    I read that article, actually, a while ago; I remember it came out around my birthday. It seems to me that what developed was "reason" more than "logic" as outlined in the study. Would it be appropriate to say that there's a difference between reason and logic?

    Reasoning is the act of providing supporting statements for your argument.
    Logic is what determines whether those statements are valid or not.

    Reasoning with sound logic:
    Guy 1: "We should hunt deer tonight."
    Guy 2: "Why? I think we should forage for berries."
    Guy 1: "We need both food and clothing; berries cannot provide clothing."
    Guy 2: "Good point. Let's go."​

    Reasoning with dubious logic:
    Guy 1: "We should hunt deer tonight."
    Guy 2: "Why? I think we should forage for berries."
    Guy 1: "It's cold, so deer are more likely to be moving and will be easier to hunt."
    Guy 2: "Good point. Let's go."
    (Never mind that deer may or may not actually be more mobile in the cold and that, by being mobile, would be easier to hunt.)​
  12. Nov 17, 2011 #11
    Language is the first logical system that we aquire as children. Each language has it's own coherent set of rules that all speakers of the language use, unconciously. The ability to think logicaly likely developed historically alongside the ability to speak.

  13. Nov 17, 2011 #12


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    I really don't appreciate the notion of logic as somehow accidentally applying. It is as if you somehow could imagine a logical argument not being valid, but at the same time accept that it is since logic has served you in the past. Or that it accidentally worked, hence our brains evolved to work around this assumption.

    It's nothing like that.

    Logic isn't arbitrary in the sense that it somehow works, and we don't know why.

    Logic is part of the structure of language. For example: that we can infer A from (not (not A)) is because that is how the word "not" is used, it is how the word functions in conjunction with propositions.

    That fact is arbitrary in the sense that "not" didn't have to function that way. But if it didn't, then "not" wouldn't have the same meaning as it does now. One could imagine that double negation was to be interpreted as strong denial, such that the proposition (not not A) would be interpreted as (not A). This isn't a challenge to logic, but a alternative sense of the word "not".

    The logical rules are simply a reflection of the function our words have in conjunction with propositions. Therefore they are absolute and undeniable, but not in the sense that we couldn't have a different logic. Rather, a different logic would require words with different meanings. But this would give a different sense of "proposition". Furthermore, the reason our logic seem undeniable is not because our words function correctly (as if they could function incorrectly), but because we know how they function. We know how to apply "not". Therefore, denying a logical argument is like denying the meaning of our words. That is, denying the way we know to apply them. That's the source of the firmness of logic.
    Last edited: Nov 17, 2011
  14. Nov 18, 2011 #13


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    You seem to be arguing a Wittgenstein "meaning is use" approach here. The atomic elements of logic (the operations and quantifiers like: "not", "or", "and", "there exists", "for all") are true by definition. They are true because that is the system as we invented it.

    Yet there is still seems to be a need to justify this invention. We use these syntactic elements not simply as an arbitary custom, but because they seem fundamentally true to us. So what is the basis of that truth?

    As Tarski's undefinability theorem argues, this basis is not going to be found within the terms. We can't use the logical elements to prove themselves.

    But still, there seems to be a rationalistic support for them (arguments from reasonableness) as well as empirical support (arguments from observation).

    The empirical support comes from successful modelling of the world. If we think about things this way, we can see that it is a form of analysis that gives us control over the events described.

    And we can trace a history of improvement in such modelling. Animal minds evolved to be pretty successful at controlling their worlds. There is a proto-reasoning in that animals are good at forming effective habits. Then human language lifted reasoning to another level. Every sentence is a statement of cause and effect (subject, verb, object, or "who did what to whom"). Then philosophers, principly Aristotle, refined the business of reasoning into logic - a mathematical strength syntax for doing world modelling. A formal model of causality.

    And it was only this last bit that has been consciously rational in its justification. As with the law of the excluded middle, there was a careful and step-by-step development that pared away the arbitrary so as to leave only what could not be denied as correct - correct through self-consistency, symmetry, irreducibility. Or if we look really closely, through the argument of dichotomy. The arrival at metaphysical categories that are complementary pairs, formed by demanding that they are mutually exclusive, jointly exhaustive.

    (I know I keep saying the same thing, but it is the very thing that history has seemed to forgotten - for reasons closely to do with what logic has become.)

    So for example, the law of the excluded middle itself was the demand that statements be framed in ways that they are either true or false. Ordinary language always has to be about something, even when referring to unicorns. So semantically, truth and falsehood are rather fuzzy judgements (unicorns might exist undiscovered, the idea exists at least, the component parts of horse and horn exist as facts it seems, etc). But Aristotle cut the syntax free of the semantics. He said if statements can be constrained so that all vagueness, indeterminacy, etc, could be eliminated, then would have a purely syntactic status based on the binary dichotomy of true~false.

    So there was a rationalistic process of clarification. In real life - based on empirical experience and the inescapable vagueness of all semantic claims - nothing is actually completely false or true in a way that we "definitely can know it" via our experience. But syntax is where we get to make things true by definition. We say, there just exists this general dichotomy of true~false as a global constraint on properly formed (ie: logical) statements. Of course, this leap from experience to true by definition is immediately then justified in pragmatic terms - we find that this further step works to improve our modelling of reality. But a leap still gets taken.

    (Again, all this is a re-hash of Pattee's epistemic cut, Rosen's modelling relations, and other modern schools of epistemology - even though these guys are scientists rather than philosophers :devil:.)

    What then of the atomic elements of logic syntax then - the fundamental vocabulary of "not", "or", "and", "there exists", "for all"? Where are the dichotomies that are the rational basis of these?

    The quantifiers of "there exists" and "for all" are simply the standard metaphysical dichotomy of particular~general (or one~many, specific~universal, local~global - the other allied ways of saying the same thing). "There exists" is a statement about particular existence, and "for all" is a statement about general existence.

    You then have the three qualifiers of negation, addition and exclusion. In general, they rely on the atomistic hypothesis. This is the belief that reality reduces to atoms in a void. You have located objects with properties whose existence is irreducible. And they then freely do their thing in a void - in an a-causal backdrop that just is, and does not itself influence the goings on happening within it.

    So the metaphysical dichotomy is atom~void. And it must be noted that it is not at all realistic in fact. The demand is that all causality is reduced to a collection of parts. The whole exists only in a way that does not actually count. But still, this was a useful point of view. It certainly did not capture the whole of the truth of reality, but it was a stunningly successful partial story because it was so simplified, and allowed so much to be ignored.

    A syntax of logic was then developed from this metaphysics. A leap was made that treated atomism as complete truth.

    Atomism is based on the idea of local additive construction - material cause + effective cause in the Aristotelean scheme.

    So negation is legitimated by the binary of atom or void - there are only two possible choices, that something exists, or that it does not exist.

    Addition is legitimated by the atomistic irreducibility of existence and properties. If something exists, then that doesn't change. So two things coming together are the sum of what existed.

    Exclusion is legimated again by atomism in that if something definitely exists at a location, then nothing else can exist at the same place. It becomes a definite case of either/or.

    So atomism captures a particular mental image of causality (as causal atoms behaving completely freely within an a-causal void - ie: material/effective cause). And then rationalistic argument extracts a syntactical basis for logic from this. If atomism were true, these must be its consequences. The most basic qualifications of a state of affairs will be in terms of negation (does something exist - yes/no?, addition (what exists can only be summed - a conservation principle for atomistic essences), exclusion (if something exists at a spot, then nothing else can exist at the same spot).

    Again, this is a syntax that works. But which is also rationally invented at the final step. An epistemic cut has to be made between the semantics and the syntax so as to have a syntax. At some point, we cut the cord. We say atomism seems enough the empirical truth of reality to just make the jump and treat it as actual known truth. And get on with using this invented tool of reasoning.

    Of course, as I also keep saying, atomism is itself one half of a metaphysical dichotomy. There is also the holistic or systems view of causality. In ancient Greece, the two views were still being entertained. If you read Aristotle's metaphysics, it is largely an attempt to reconcile the two apparent extremes of causality. This is why he talked about four causes - including formal and final cause in his scheme. The "causes of the void" we might say. The global, top-down causality of constraints on local freedoms.

    But the simple logic represented by atomism took off. The other possible half of logic has languished. It has flared in the work of Hegel and Peirce. It is there again in systems science and semiotics and other attempts to frame a more holistic model of causality.

    So there is a "mental image" of holism, just as there was of atomism. But it has not been developed into a completely stripped-down syntax. Although see this paper for some playing around with the possibilities.

  15. Nov 18, 2011 #14
    I'm not sure; but, you may be mistaking mathematics for logic here.

    This is why we cannot depend on dichotomies (or what you call metaphysical dichotomies, unbeknownst to me), they are a result of the LEM which is bound with our "internalistic scaffolding of logic". Where you latter criticise logical atomism for its over-simplicity I think it avoids creating strict metaphysical dichotomies which you present as our only way of understanding things (or I have misunderstood your position or lackof).
  16. Nov 19, 2011 #15


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    Apparently so. Are you suggesting that atomism does not depend on the notion of the void?
  17. Nov 19, 2011 #16
    I just don't see how you draw out these dichotomies.
  18. Nov 19, 2011 #17


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    It is important to distinguish:

    inductive reasoning; reasoning concerning causality,


    logical arguments.

    It is not the same thing, and should not be mixed up.

    There is no need nor reason to verify a logical argument. When we state a logical proposition, we decide that it is a logical proposition subject to reasoning by logic rules.

    Reasoning of causal consequences are not logical arguments, they require radically (categorically) different means of verification.

    Let's take the example mentioned some time ago in this forum: consider the situation; 'A man is standing in the doorway of a room.' We could argue that "he is in the room", and that "he is not in the room". But when we consider both of these alternatives as valid in some sense, we are at the same time deciding that we are not stating logical propositions.

    "The man is standing in the room" as a logical proposition does not refer to the man, the room, nor the meaning of 'standing in the room'. As a logical proposition it is entirely separate from these things.

    We use logical rules as a criteria for determining whether a means of verification of a statement is valid. In other words, if our means of verification for determining whether the man is in the room allowed us to draw both conclusions, namely "he is in the room" and "he is not in the room", we will automatically dismiss it. We require that the meaning of "standing in the room" must adapt itself to this.

    Logic is in this sense part of the structure of language, it is our rules governing propositions. As they don't refer to anything outside of language, it need not be verified. A good illustration of this is the fact that we would be perfectly fine operating with a different type of logic.
    Last edited: Nov 19, 2011
  19. Nov 19, 2011 #18


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    It's in the definition: mutually exclusive, jointly exhaustive. It gets easy with practice.
  20. Nov 19, 2011 #19


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    All you are pointing out here is that logic is pure syntax, and has been scrubbed clean of semantics. Which is what I said.

    But the OP was about the development of logic. Which was what I was addressing.
  21. Nov 19, 2011 #20
    But, my point is the method. If I understand this properly, in simple terms you are taking the inverse of anything(?)
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