I don't even know where to begin here, Michael. Your bafflement probably comes from psychology textbooks typically being vague and uninformed about the distinction. Let me put the question the other way for you: Why would you regard them as being the same, putting them both under the very vague heading of "reasoning," rather than making then entirely distinct categories.
There is a formal process that explains most kinds of deductive logic. We know exactly how to get validly from premises to conclusions (where "valid" means that truth will be "preserved" from premises to conclusions). That formal process began to be uncovered in Ancient Greece (and probably before), but was still divided between "propositional" and "syllogistic" (quantified) branches until Bertrand Russell and Alfred North Whitehead combined the two in the early 20th century (in their Principia Mathematica). Since then, deductive logic has focused mostly on extensions of that (2nd order logic) and various "deviant" logics (modal, multi-valued, relevance, etc.). The problem is that deduction is always the unfolding of specific knowledge that was "folded" into knowledge we already (believed we) had. If all ravens are black, then of course the raven in my backyard right now is going to be black. Sometimes deductions are not that obvious -- they lead to realizations of implications we did not previously recognize -- but it can never result in truly new knowledge, which is what the "new" scientists of the 17th century aimed to produce. Induction is an entirely different ballgame. Although Aristotle did some primitive work on it, how it actually operated was pretty much a mystery until the mid-19th century. The general idea was that, somehow, the collection of enough individual observation of some phenomenon would eventually add up to evidence sufficient for one to make a general claim (Francis Bacon is often credited with a view like this, though his position was actually more sophisticated). David Hume famously "exposed" the whole thing by noting that nothing of that sort was ever going to work because, no matter how many positive instances one had collected, it would only ever take one additional negative instance to bring down the whole thing (classically illustrated by the discovery of black swans in Australia -- all the white swans Europeans had observed to that point didn't mean a thing, and the whole project of determining that "All swans are white" collapsed in an instant). By the bye, Popper's famous "falsificationism" is an effort to take Hume seriously by attempting to convert science into a form of deduction by only attending to refuting instances (which, unlike confirming ones, are deductively valid). Although it evaded the old Humean "problem of induction," it left science with no way to make positive statements about the world (which, clearly, it does, more or less successfully, all the time). Popper was not the only one to attempt to turn science into a form of deduction. Carl Hempel did as well, with his Deductive-Nomological theory. It had its problems as well (in what way does observing the prediction in the conclusion contribute to the truth of the covering law in the premises? Problem of induction again), but it did give science a way to make positive claims again. Induction finally began to get formalized when it was wedded to probability theory. There are bits of this in the 18th and 19th centuries, but it didn't really get going until the 20th. Probability theory solves (or, at least, addresses) the problem by providing a framework for rigorously deducing conclusions that have probabilities in them (and so the uncertainty is quantified). That is, one may not be able to conclude that "All swans are white," but I can conclude that there is, say, "a probability of .8 that the next swan I see with be white." There are some names psychologists will recognize in this story: Ronald Fisher and Karl Pearson, among others. Unfortunately, psychology seems to be stuck in the frequentist formulations of these folks and, despite repeated efforts since the 1960s, can't seem to move on to more adequate Bayesian formulations of the late 20th century (though several other sciences have). There is also a third form of reasoning that is often conflated with induction. It was identified by the late 19th-century American scientist-philosopher-semiotician Charles Sanders Peirce. He noted that the process by which we attempt to inductively confirm a hypothesis with evidence (induction) is entirely distinct from the process by which we choose a particular hypothesis to be confirmed in the first place. Peirce labeled the latter process "abduction." Psychologists, to the extent that they pay attention to this process at all, tend to conflate it with induction. There is no reason, a priori, to expect that these processes will be underpinned by the same psychological processes. Indeed, the natural assumption would seem to be that they are pretty distinct, psychologically. That is why cognitive textbooks should separate them (probably into different chapters). I hope this helps. Chris --- Christopher D. Green Department of Psychology York University Toronto, ON M3J 1P3 Canada [email protected] http://www.yorku.ca/christo/ ========================== On 2012-03-16, at 8:14 AM, Michael Britt wrote: > A typical cognitive psyc chapter explains these two terms and the difference > between them. I'm always left with a feeling of "Okay. Interesting, but so > what?". My apologies to those who have studied logic. But aside from being > fodder for a multiple choice question, ("Which of the following is an example > of inductive reasoning?"), and excuse the emphasis on pragmatism, but why do > we teach these two concepts? > > > Michael A. Britt, Ph.D. > [email protected] > http://www.ThePsychFiles.com > Twitter: mbritt > > > > > > > --- > You are currently subscribed to tips as: [email protected]. > To unsubscribe click here: > http://fsulist.frostburg.edu/u?id=430248.781165b5ef80a3cd2b14721caf62bd92&n=T&l=tips&o=16755 > or send a blank email to > leave-16755-430248.781165b5ef80a3cd2b14721caf62b...@fsulist.frostburg.edu --- You are currently subscribed to tips as: [email protected]. To unsubscribe click here: http://fsulist.frostburg.edu/u?id=13090.68da6e6e5325aa33287ff385b70df5d5&n=T&l=tips&o=16761 or send a blank email to leave-16761-13090.68da6e6e5325aa33287ff385b70df...@fsulist.frostburg.edu
