Deutsch’s A new way to explain explanation

David Deutsch: A new way to explain explanation TED talk.

The search for hard-to-vary explanations is the origin of all progress. It’s the basic regulating principle of the Enlightenment So, in science, two false approaches blight progress. One is well known: untestable theories. But the more important one is explanationless theories. Whenever you’re told that some existing statistical trend will continue, but you aren’t given a hard-to-vary account of what causes that trend, you’re being told a wizard did it.

That the truth consists of hard to vary assertions about reality is the most important fact about the physical world.


Deutsch is well respected and quite succinct. Popper says much the same, but people tend to focus on his headline criterion of falsifiability.

The key issue seems to be one which Keynes discusses in his mathematical Treatise. Some people suppose that regularity is natural, and it is irregularity that demands an explanation. Thus where a regularity is observed, they assume – ‘pragmatically’ – that it will continue, unless there is a specific reason why not. For example, in economics it has been assumed that trends can be extrapolate without considering the underlying situation. The alternative, with Keynes and Deutsch advocate, is to suppose that regularities are the result of some ‘systems’, and that one can only rely on extrapolations if there is reason to think that the systems will be maintained. This in economics one only relies on trends continuing when the relevant agencies (e.g. central banks) have the ability and will to sustain their preconditions.

It seems to me that most theories have aspects that are easy and hard to vary, and that the aspects that are hard to vary are true (in Deutch’s sense) subject to their easy to vary aspects being true. Proper mathematical theories are hard to vary in all their essentials, but (as Keynes points out) the ‘truth’ of financial mathematics is very conditional. In a sense, then, while financial mathematics is what Deutsch calls wizardry,  there are within it useful aspects that are ‘true’.  The key is to recognize the difference. Part of this is to recognize how much of financial mathematics is truly  mathematics and how much is wizardry, using mathematics to bamboozle.

Dave Marsay


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