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Justification for Logic?

makerowner
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Posted 06/20/08 - 05:15 PM: Subject: Justification for Logic?	#1
I'm posting this here because I'm asking more about the epistemological justification than about logic itself, but if it fits better in Logic, feel free to move it. As far as justification goes, I tend to sympathize with infinitism (that is, that an infinite regress of justifications is possible), but I've been trying to come up with a justification for believing in logic, and I can't. Why should we believe that A→B, B→C, ∴ A →C is true? (Without presupposing the laws of logic, I mean) Is our justification for believing in logic just an empirical observation that if you start from true premises and follow these rules, you'll end with a true conclusion?
For philosophy, Socrates, if pursued in moderation and at the proper age, is an elegant accomplishment, but too much philosophy is the ruin of human life. Even if a man has good parts, still, if he carries philosophy into later life, he is necessarily ignorant of all those things which a gentleman and a person of honour ought to know.

Reformed Nihilist
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Posted 06/20/08 - 05:24 PM:	#2
makerowner wrote: Is our justification for believing in logic just an empirical observation that if you start from true premises and follow these rules, you'll end with a true conclusion? I would suggest that is exactly the case.
Nobody ever became a famous philosopher by being a champion of ecumenical hybridism Daniel Dennett Freedom Evolves

Jehu
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Posted 06/20/08 - 05:30 PM:	#3
The rules of formal logic are derived from a single principle â€œThe principle of Identityâ€, which is the â€˜first principleâ€™ of thought: that a thing is the same with itself, but different from another thing. Without that we accept the primacy of this one law there can be no rational enquiry, for without that this law holds, there can be no language at all. This is why we may have as many different names for a single thing as we like, but we cannot assign the same name to two different things; for then there would be no basis upon which to communicate.
It is not that which the eye can see, but that whereby the eye is able to see, that is the true reality.

makerowner
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Posted 06/20/08 - 05:33 PM:	#4
Reformed Nihilist wrote: I would suggest that is exactly the case. But why do we feel so certain about logical judgements? They don't "feel" the same as inductive judgements of the sort "well, every other time I've started with this input and done this process, I've gotten this result, so I'll probably get the same this time."
For philosophy, Socrates, if pursued in moderation and at the proper age, is an elegant accomplishment, but too much philosophy is the ruin of human life. Even if a man has good parts, still, if he carries philosophy into later life, he is necessarily ignorant of all those things which a gentleman and a person of honour ought to know.

NoSoul
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Posted 06/21/08 - 09:01 AM:	#5
I think those are very good questions & observations. I would suggest, as implied already, that logic springs from a type of intuition. One problem with that is that it might be fallible; but the fact is when a logical mistake occurs, we usually behave as if the problem lies in the argument or the arguer, not with logic itself. It's almost enough to make a Platonist out of some of us: As if intuition has a direct, objective connection to reality, not merely is an instinctual, provisional "guess." (I would never categorically call myself a Platonist, though. That still seems weird & unscientific. Then again, "seems' indicates yet another intuitionist component.)
Firmly tie the mind, resembling a mad elephant, to the strong pillar of its perceptual content, with the rope of contemplative inspection, and gradually tame it with the hook of discrimination. -- Buddhist Handbook, Salamander Press To the poet and sage, all things are friendly and hallowed, all experiences profitable, all days holy, all men divine. - Nietzsche/Emerson

kNoctis
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Posted 06/22/08 - 06:07 PM:	#6
We make the inference that our use of logic is justified because our empirical observations seem to match our predictions. That inference is deemed valid, and therefore true, because it adheres to certain rules of logic. But those are the very same rules of logic we are attempting to validate. Therefore, the argument is circular. Any attempt to justify logic will inevitably result in an illogical inference, either because it is a simple non sequitur - i.e. a purposively irrational attempt at justification, ex. mysticism, emotionalism, subjectivism, etc.., OR because it is a circular argument. Give it up.

Thinker123
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Posted 06/25/08 - 08:45 AM:	#7
makerowner wrote: I'm posting this here because I'm asking more about the epistemological justification than about logic itself, but if it fits better in Logic, feel free to move it. As far as justification goes, I tend to sympathize with infinitism (that is, that an infinite regress of justifications is possible), but I've been trying to come up with a justification for believing in logic, and I can't. Why should we believe that Aâ†’B, Bâ†’C, âˆ´ A â†’C is true? (Without presupposing the laws of logic, I mean) Is our justification for believing in logic just an empirical observation that if you start from true premises and follow these rules, you'll end with a true conclusion? Logic can't justify logic itself as this is circular reasoning. We could say that the pragmatic results justify logic, but then what is the justification of pragmatism? Pragmatism itself? Then another circular reasoning we have. Faith? Well, there are many different faiths. So which one to choose? Any suggestions?

Simple Occam
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Posted 06/25/08 - 12:31 PM:	#8
Logical relationships hold among sentences. But what are sentences other than linguistic representations of what we experience in perception or imagination? For me, all knowledge is empirical, so I wouldn't say its "just" an empirical observation, as if something non-empirical were somehow superior. Logical truth or falsity derives solely from the meanings of the "operator" words that define logical relations such as 'and', 'or', 'not', 'if', 'then', etc. Also terms like 'all', 'none', 'some' etc. have meanings that imply logical relationships among terms and sentences. To ask for any further justification of logic is like asking why 'and' means what it does. "That a thing is the same with itself, but different from another thing" is not a self-evident truth at all but an empirical generalization built up from observing many things and noticing that they are different from one another in SOME way (size, shape, color, smell, etc) or, if not different in any of those ways, in spatial location. It's an empirical truth about the nature of reality, not something true by definition or due to rational intuition. Nor is it true because otherwise "there would be no basis upon which to communicate", as Jehu writes. It's true because matter is particulate in nature, meaning we live in a pluralistic universe wherein many distinct substances are separated from one another by space and no 2 of them can coincide with the same location in space at the same time. So, even if 2 things had exactly the same properties or qualities, each would be "the same with itself, but different from another thing" because they coincided with different parts of space. If they had all the same properties AND coincided with the same parts of space, they would be the same thing with itself, not different from another thing. But this is ontological thinking that comes from common sense experience and the meanings of logical terms... NOT a self-evident Why should we believe that Aâ†’B, Bâ†’C, âˆ´ A â†’C is true? If I go to work, I'll get paid. If I get paid, I can buy a new car. Therefore if I go to work I can buy a new car. The validity of the logic is recognized in the FACT that no matter what terms we subsititute of A, B and C, the meanings of those logical terms imply that the statement will be true when we go out and look in the world or even just imagine what would happen as a result of the substitutions.

Thinker123
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Posted 06/26/08 - 08:07 AM:	#9
Simple Occam wrote: Logical relationships hold among sentences. Please explain. Logical truth or falsity derives solely from the meanings of the "operator" words that define logical relations such as 'and', 'or', 'not', 'if', 'then', etc. Who or what gives the meaning to the "operator" words? Are these things found in nature outside of the mind? What color or shape are 'and', 'or', 'not', 'if', 'then', etc. How much do the weight? Where and when are they physically located? How long are they (in feet or metres)? Also terms like 'all', 'none', 'some' etc. have meanings that imply logical relationships among terms and sentences. To ask for any further justification of logic is like asking why 'and' means what it does. Exactly. Why does AND means AND, not OR? "That a thing is the same with itself, but different from another thing" is not a self-evident truth at all but an empirical generalization built up from observing many things and noticing that they are different from one another in SOME way (size, shape, color, smell, etc) or, if not different in any of those ways, in spatial location. It's an empirical truth about the nature of reality, not something true by definition or due to rational intuition. Sunrise, sunset, hallucinations are emperical truths as well... Yet now, after millenia of ignorance we "know" that they are merely apparent truths and that ultimately it is the other way around (helio not geo centrism).

Cuthbert
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Posted 06/26/08 - 08:26 AM:	#10
makerowner wrote: I tend to sympathize with infinitism (that is, that an infinite regress of justifications is possible), but I've been trying to come up with a justification for believing in logic, and I can't. Why should we believe that Aâ†’B, Bâ†’C, âˆ´ A â†’C is true? Then I think Lewis Carroll solved your problem. A->B B->C What licences us to draw the conclusion - A->C? The licence is a rule of inference, thus: (A->B) & (B->C) -> (A->C). Now that rule, together with the first two statements licences us to draw the conclusion. But hang on - what licences that rule of inference itself? Clearly, another rule of inference, thus: (A->B) & (B->C) & [(A->B) & (B->C) -> (A->C)] -> (A->C) And so on ad infinitum. And if you don't mind an infinite regress of justifications, then you're sorted. Lewis Carroll, "What the Tortoise Said to Achilles," Mind 4/

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