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Theory of Rationality vs. Formal Logic
A Gilbert Harman production

Theory of Rationality vs. Formal Logic

Timothy
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Posted 09/28/09 - 02:40 PM: Subject: Theory of Reason vs. Formal Logic	#1
I've been reading a book called Handbook of the Logic of Argument and Inference. The basic point of the book is to make a case against classical deductive logical apparatus as a proper theory of human reasoning, thus strengthening the case for a different approach in tackling such a theory (mostly, an interdisciplinary approach invoking empirical psychology, forensics, argumentation theory, and a whole bunch of stuff). A chapter of the book is written by Harman, where he shows how classical logic fails to give a proper model for human reasoning. Note that rational decision theory, as employed in economics, is also rejected as a proper model for human reasoning. The arguments are persuasive: he notes, for example, that there is no normativity involved in a deduction, since you're not obliged to accept the conclusion of a deductive argument, or you could believe the premises without believing the conclusion for a whole bunch of different reasons (being unconscious of the logical implication, or not being able to infer the conclusion because it's a very difficult proof, etc), without being irrational. That is, you could be rational and not necessarily reason as if following deductive rules of classical logic. He makes the point even farther, making a case against "ideal" reasoners as operating solely under the principles of classical logic. The main argument against the idealist approach is that it abstracts the beliefs of a subject from the context that originated those beliefs, and when something contradicts a belief, an ideal reasoner would have no way to resolve the inconsistency, since there's no purely logical way of determining which of the beliefs is wrong (Harman assumes that we can solve this in the case of everyday reasoning mostly based on the origins of the belief being contradicted). Is anyone else uncomfortable with this position? I have been unable to express a concrete rebuttal.
"Neither Aristotelian nor Russellian rules give the exact logic of any expression of ordinary language; for ordinary language has no exact logic." P.F. Strawson

realistcat
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Posted 09/28/09 - 04:23 PM:	#2
I'm a former logic teacher. I used to teach symbolic logic. At a certain point I came to see this as not a useful way to approach logic. There are in fact many invalid inferences in natural languages that can be "validated" by the classical Frege/Russell logic (the logic taught in colleges all over the world). Moreover, deductive logic has a limited usefulness. The far more important form of reasoning for human life and knowledge is abductive reasoning...inference to the best explanation. Abduction functions very differently than formal deductive logic. Deduction is needed in conjunction with abduction because you can use various forms of reasoning, including deductions, to work out what would have to be true for a hypothesis to be plausible, and when you test the hypothesis you use chains of reasoning including deductive inferences. Diagnosis and forensics use abductive reasoning. It's also useful to distinguish reasoning from argument. Argument has a social function and occurs in a social context. We present arguments to people to persuade them to believe things or go along with us in some proposed policy or course of action. A reasoning you could think up in solving some problem yourself. It's well known that there is a distinction between the psychological persuasiveness of arguments and their cogency. But cogency is hard to define. Cogency has to do with what you "ought" to be persuaded by. For example, how much energy should someone consume in trying to obtain evidence for some premise? Well, this depends on how important the issue is to them. So what one "ought" to believe isn't solely a matter of the cogency of the reasoning but depends upon the practical interests of people. But people who recommend "informal logic" also don't have much to go on. The problem is that this relies on the idea of so-called "fallacies." But the fact is, there is no theory of what a fallacy is. For centuries philosophers have merely replicated Aristotle's list of "fallacies" without ever developing a theory to explain why something is a fallacy. A fallacy is supposed to be a mistake in reasoning of some kind, but Aristotle's list is a grab bag with no theory as to how to apply the ideas. This is discussed in excellent detail in the anthology "Fallacies" edited by Hansen and Pinto. Edited by realistcat on 09/28/09 - 04:34 PM

Timothy
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Posted 09/28/09 - 09:06 PM:	#3
Great reply, realistcat Harman also points out that it is abduction, not deduction nor induction, what seems to be closer in modeling the actual human reasoning. I don't know much about abduction as a theory of reasoning, but its adequacy is beyond the point of this thread. Your distinction between reasoning and argument is, as far as I see it, correct, and is analogous to the remark I made about Harman noticing how certain normativities (i.e. what ought to be believed, etc.) don't hold in the case of classical logic. What I find most discomforting is Harman's distinction between deduction and reasoning. He sees deduction as a purely logical relationship between certain structures, i.e. as logical implication. This he distinguishes from inference. Logical implication is no inference. Inference is a psychological process that constitutes the basis of reasoning. There's no "deductive" reasoning opposed to "inductive" inference. Deduction is implication, which is not to be identified with inference. This I find bothersome. I would gladly grant that classical logic is not a comprehensive model or theory of all process of rational reasoning; but I would like to think that it is a model for a fragment of human rational reasoning, and I would like to call it "deductive reasoning". There are, after all, elements of the classical theory that ought to form part of a theory of rational reasoning (perhaps not practical rationality though), such as consistency, the notion of proof, etc. What keeps me from phrasing a convincent rebuttal to Harman is that he recognizes these features as helpful in developing a theory of rationality, but still considers them insufficient to give an account of actual reasonings. The point could, perhaps, be settled by empirical research.
"Neither Aristotelian nor Russellian rules give the exact logic of any expression of ordinary language; for ordinary language has no exact logic." P.F. Strawson

swstephe
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Posted 09/28/09 - 09:51 PM:	#4
It sounds like the book is trying to sneak in an argument based on another implied fallacy which makes it kind of an ironic statement. It is making a statement that human brains don't generally operate on classical logic. Well, that's no surprise. Cognitive psychology has consistently shown that human brains are probably connectionist fuzzy neural nets tied to emotional valuation systems. It would be a mistake to assume "classical logic is wrong because humans don't think that way". Logic is an important tool that the brain can use to help define objective facts. Like realistcat says, we can use classic logic to persuade others toward a certain conclusion, but the ultimate authority of how we tend to think isn't that formal. Is the book really saying that classical logic is someone "bad", or is it saying that there is probably a whole new field of logic which we have only begun to explore which is closer to human reasoning? I think the latter would be more true, but maybe being controversial sells more books. If induction or abduction, (which I think has already been successfully been used in experimental models in AI, fuzzy logic, and connectivist systems), is useful for human thinking, is it possible to codify this logic in a way that is useful for persuasion and automation? For the time being, classic logic has served formal processes quite well and revision would only be warranted by creating a more efficient, useful, system from other systems of logic. In AI research, fuzzy models seem to only be useful in some narrow cases, and ultimately become a disappointing effort when they can always be reduced back down to classical logic models anyway.
Ethics is the measuring of morality. Morality is the measuring of good. Good is the measuring of benefit. Benefit is the measure of values.

Timothy
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Posted 09/28/09 - 10:05 PM:	#5
swstephe wrote: Is the book really saying that classical logic is someone "bad", or is it saying that there is probably a whole new field of logic which we have only begun to explore which is closer to human reasoning? The idea is that classical logic is not a model at all of rational reasoning. That is, deductive relationships do not model the rational agent's inferences. So the point isn't as naturalistic as it seems (I'm to blame due to my initial phrasing). It's not that human brains actually do not operate as following deductive rules of classical logic, but rather that the question of rationality is not settled by an appeal to classical logic, i.e. classical logic is not a theory of rationality. Harman goes farther in saying that classical logic isn't even a part of a theory of rationality. I find this bothersome. So yeah, the latter point would be closer to the book's spirit. There would be a different type of logic, i.e. a type of informal logic, produced by a different interdisciplinary melting pot, that would adequately constitute a theory of rationality and valid (yet not deductive) reasoning. swstephe wrote: If induction or abduction, (which I think has already been successfully been used in experimental models in AI, fuzzy logic, and connectivist systems), is useful for human thinking, is it possible to codify this logic in a way that is useful for persuasion and automation? These people seem to think so (the book is a compilation of essays from a whole bunch of different people; I think you can check it out on amazon). This seems to me to be alright, yet I'm unconvinced about Harman clear-cut distinction between reasoning and deduction as presented in classical logic.
"Neither Aristotelian nor Russellian rules give the exact logic of any expression of ordinary language; for ordinary language has no exact logic." P.F. Strawson

unenlightened
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Posted 09/29/09 - 09:29 AM:	#6
Timothy wrote: Is anyone else uncomfortable with this position? What can one deduce from one's discomfort? Or should I ask, can one become uncomfortable by deduction? ...when something contradicts a belief, an ideal reasoner would have no way to resolve the inconsistency, since there's no purely logical way of determining which of the beliefs is wrong. I heard somewhere that the mark of genius is to be able to tolerate the discomfort of inconsistency without rushing too quickly to a resolution. In math, one proceeds commonly by command. Do this, make a distinction, let N be... Perhaps there is an aesthetic of commands and questions according to their fruitfulness of consistent deductions and comfort. I suppose the supreme discomfort is when one's most fundamental beliefs cannot be resolved " But surely light cannot be a wave and a particle..." Concrete rebuttals are set in stone which turns out in the final analysis to be some improbable quantum weirdness that we have no access to. In the beginning was the deed and perhaps it is the deed that justifies belief. Never mind if you can reconcile with your understanding imaginary numbers - look what you can do with them. And in the doing one becomes more comfortable. I must have a look at that book, it sounds interesting.
...most of our actions are the result of the past, or according to a future ideal. That's not action, that is just conformity. J Krishnamurti "Philosophy, to the Philistine, is an evolutionary process, watched over by some sort of brisk dynamic Providence, and culminating in the supreme insight of modern thought." John Cowper Powys

Timothy
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Posted 09/30/09 - 12:01 PM:	#7
I guess what I find to be somewhat wrong is Harman's assertion about classical logic as not being a theory of rationality at all, i.e. it has a completely different subject-matter. What I feel is correct is to deny that logic provides a comprehensive theory of rationality (theoretical plus practical?), yet maintain that it at least gives a model of a fragment of rational happenings, i.e. specific deductive reasonings. In this sense, logic could be a tiny part of a larger theory of rationality.
"Neither Aristotelian nor Russellian rules give the exact logic of any expression of ordinary language; for ordinary language has no exact logic." P.F. Strawson

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