Limits to Reason

May 8, 2017 – 10:25 am
Colin McGinn had a comment on the human tendency to irrationality, partly wondering why people are so irrational given that “human irrationality can seem the oddest and least adaptive trait of the species,” and accepting that “we need to know what causes irrationality and what we can do to fix it.” I replied, and I thought I might as well save that reply here:

There is a general assumption that rationality is adaptive – and your claim that irrationality looks maladaptive would be a version of that – but Stephen Stich in his book The Fragmentation of Reason went through a selection of the arguments that he could reconstruct for that position and found them all pretty badly wanting. Even without reviewing his counterarguments, it must be pretty clear that if rationality really was so advantageous it wouldn’t have taken 3 billion years to arise in the current evolutionary process; so the mere fact that we are as rational as we are (or can be) is something that we should marvel at.

There are, in fact, very good reasons why a restricted irrationalism might be an optimal evolutionary strategy, and why we should therefore expect people to be irrational at least to some degree. (Cherniak’s Minimal Rationality has more thoughts on this topic.) The principal reason follows from the fact that we cannot expect any natural system to be a perfect reasoner. For one thing, there are physical limits to deductive capacities in any finite device. Since we can’t be perfect reasoners, and there are time constraints on the reasoning that we can indulge in, it makes sense that we would be designed to take shortcuts (as Breako mentioned.) These shortcuts get us answers that are good enough and tend to err on the side of safety. That is an evolutionarily superior strategy to one which involves just reasoning – even reasoning according to the most reliable rules of induction or deduction. There’s a lot of work on this sort of thing following on from Kahneman and Tversky’s experiments. (It’s not even the case that ‘knowing the truth’ or ‘disbelieving falsehoods’ has an adaptive value in itself. One very annoying finding is that people who are religious believers are relatively more successful and happier than others – and it doesn’t seem to matter what they believe in, just that they believe.)

In this respect then, we are really in the same position as many other animals on this planet, having a certain degree of rationality, far from perfect, and trying our best to get along with what we’ve got. One way to see how our limits affect us, and why we should be cautious and humble in applying our reasoning powers to complex questions, is to look further down the Great Chain of Being and see how the situation looks for those ‘lower’ creatures. Take dogs for example. Do we think dogs would be better off if they were stripped of their instincts and the traditional social structures of the pack, and were left to attempt to reason out their life choices? Would such animals be able to set appropriate goals for themselves? And for any choices they made, would they be competent to reason out the proper means to achieving them, or would they fail because they are just not smart enough and don’t have a proper understanding of the way the world is? And if we can accept that those animals have that problem, and that we are essentially just as far as they are from perfect rationality, then does it not follow that we will have that problem too?

I guess the upshot of this reasoning, if it can be trusted, is that we don’t really know when deliberate reasoning is the appropriate way to get to a practical conclusion. At least, we shouldn’t be so sure that more ‘rationality’ is going to be a good thing, and that people who are acting irrationally, if that means acting against the reasoned opinions of others, are necessarily doing the wrong thing.


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