Distrust in logic.

Last updated 01/26/09.

Published on: May 5, 1998

At times, reading arguments, I despair. It seems to me that the only purpose in understanding logic is to be able to defend ourselves against people attempting to bully us into "intellectual" positions.

It's common knowledge that logic doesn't produce true results unless it starts with true premises. Somewhat less commonly known is that outside of mathematics, it's hard to have a true premise about some aspect of the real world. Instead, you have a premise which is accurate to some degree. There's a tradeoff between specificity and accuracy. For example, let's say that my premise is that the sky is blue. Well, it might be now. But it's not at night, and it's not where there are clouds or haze. The more specific we get, the less general and thus less valuable a premise we have.

It is possible to reason logically with imprecise premises. Good thing too, because that's about all we have. But the results are not unambiguously true; they are true for some set of specific cases, and not true for others. We have a number of heuristic means for deciding which results are likely to be accurate enough (in our circumstances) to be useful. And some times we will be wrong.

Logic is hardly the only form of reason we use. One seldom mentioned fact is that informal fallacies of argument can be very strong heuristics. Interestingly though, logical reasoning is considered to be better than reasoning by informal fallacy. But unless there is some reason to presume the premises of the logic are good enough to give better results than those of informal fallacies, this presumption could well be mistaken. (I'll explain an exception later.)

When examining natural phenomena directly and reasoning about our own observations, we usually try to make the most accurate conclusions we can. However, others may have strong motives to convince us of inaccurate conclusions. For example, if I draw logical conclusions from a premise that is true 95 percent of the time, or if I draw conclusions from informal fallacies which, when measured against reality, are 95 percent accurate, both methods are equally accurate. But an adversary might use premises which happen to be false for a specific case of interest, or present informal fallacies which give wrong results for the specific case of interest.

So there's no special reason to presume logic is better than other heuristic methods of reasoning. Yet we usually do assume that, and for one sound reason, one special case. And that case is when logic is used either to identify informal fallacies of argument, or to identify premises which are not true.

We've already established that interesting real-world premises won't be 100 percent true. And there are very few arguments for which there are sufficiently "good" premises that informal fallacies can be omitted. So how can any argument be reliable? The answer, again, is heuristic. We employ a form of heuristic reasoning about reasoning, a meta-reasoning, called "reasonable dialog" or defeasible reasoning. Here is a technical explanation of defeasible reasoning. More readably, here is an example of defeasible reasoning applied to the history of economics.

The scientific method is the best means of minimizing these problems - that I'm familiar with. It exploits our relatively good reasoning about direct observations by insisting that others be able to make the same observations, and that the reasoning be based on those observations. Still further, it tends to require that the conclusions be defeasible. Social penalties enforce those rules.

But let's head back to my initial despair now. Innumerable religions, philosophies, scientisms, and pseudosciences attempt to wear the mantle of "logic" to convince us of their claims. Our lives are strongly affected by these. Consider for example the notion of man as an economic maximizer which underlies much economics modelling (especially in policy prescriptions). Bad premise. Consider the bad premises of Objectivism and libertarianism. Consider the vast literature of religious apologetics, which is laden with innumerable bad premises. All these attempt to bludgeon us with "logic" into adopting their beliefs.

The defense is logic (and other heuristics) employed in the service of skepticism. Logic about the nature of logic, knowledge, reasoning, meta-reasoning, adversarial deception, etc. It's a strategic game, with both sides employing many tactics. There's no royal road to truth, let alone to reliable knowledge. We have to fight for it, using and understanding the same tools our adversaries employ. When we win, the result is that we have some knowledge which we think is quantitatively better than the alternatives. The reward is not the "win," but the benefits we reap from applying our better knowledge. Counter image omitted.

Copyright 2001 by Mike Huben ( mhuben@world.std.com ).