The Second Version

24/11/06

Induction, Heuristics and Probability

I began with the intention of writing a post about these heuristic things, but then it expanded to deal with broader issues.

Anyway, a heuristic is a rule or procedure that most of the time but not always works or gives the correct answer. An element of uncertainty is thus inherent to heuristics.

We use heuristics all the time, even without realizing. For example, when deciding how much to drink before getting completely wasted. That's a rule born out of those times when you were puking your guts out in the wee hours, and it generally works. But not always, because response to alcohol intoxication is highly variable. Three B-52 cocktails in a row will probably wreck you most of the times, but on one special night they may not.

Induction is something that comes naturally to us humans and even inferior animals (while deduction is our exclusive). In the words of old good Steven:
Deduction is prissy; it refuses to play unless it knows it can win. It requires sufficient information of high reliability, and when that is available it yields an answer which is nearly certain. Otherwise it refuses to play, yielding nothing. Induction is more freewheeling; it deals in probabilities and works with data of doubtful quality; it judges likelihoods and comes up with answers based in inadequate data. It extrapolates. It includes guesses. And sometimes it gets the wrong answer. But it is much more broadly applicable than deduction, and can often get the right answer in cases where deduction refuses to even make an attempt.
All this is not abstract speculation, but it has important implications in the real world. Science is thoroughly based on induction (while mathematics is deductive): so it's true that evolutionary theory is not proven, in the same fashion that relativity theory and transition state theory are not deductively proven. But using induction, there is enough evidence to hold all these theories as virtually indistinguishable from facts.

A cardinal concept here is probability. How probable is that your heuristic will give the correct answer (or the wrong one)? At what probability threshold a theory becomes nearly indistinguishable from fact? At the other end of the scale, when does it become utterly unbelievable (not to say total crap)? The truth is that there are no objective, absolute answers for the two latter questions.

I see too many people, from all sides, who seems unable to realize that they're using induction and heuristics to reach their conclusions. Thus, they present them as certainties while in fact there is a margin of error. And oddly enough, many of these people don't like to be called upon that. They are ready to cast accusations of "handwringing" or "being an EUrowussie" - when they are on the right side; from the left, the reactions are just ignoring your objections and proceeding with the agenda, or accusing you of being a servant of The Man or even racist (it makes no sense).

I don't want to teach people what to think; I very much prefer to see different opinions - though I am under no obligation to like or respect any of them or to consider them all worth the same. But I'd like to give my little contribution to teach people how to think and make an argument correctly, and realizing the distinction between induction and deduction is an important part of the process.

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