Hard to Vary or Hardly Usable?
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With an account, you can revise, criticize, and comment on ideas.Deutsch’s stance in my own words:
The distinguishing characteristic between rationality and irrationality is that rationality is the search for good explanations. All progress comes from the search for good explanations. So the distinction between good vs bad explanations is epistemologically fundamental.
A good explanation is hard to vary “while still accounting for what it purports to account for.” (BoI chapter 1 glossary.) A bad explanation is easy to vary.
For example, the Persephone myth as an explanation of the seasons is easy to change without impacting its ability to explain the seasons. You could arbitrarily replace Persephone and other characters and the explanation would still ‘work’. The axis-tilt explanation of the earth, on the other hand, is hard to change without breaking it. You can’t just replace the axis with something else, say.
The quality of a theory is a matter of degrees. The harder it is to change a theory, the better that theory is. When deciding which explanation to adopt, we should “choose between [explanations] according to how good they are…: how hard to vary.” (BoI chapter 9; see similar remark in chapter 8.)
From my article:
[D]epending on context, being hard to change can be a bad thing. For example, ‘tight coupling’ is a reason software can be hard to change, and it’s considered bad because it reduces maintainability.
@edwin-de-wit recently asked Deutsch about this:
… hard to vary can also be a property that you don’t want. Sometimes they say that complicated systems are just so entangled that they’re no longer changeable. You could call that hard to vary but it’s not a property you pursue.
Deutsch’s reply:
Quite so. So hard to vary is about explanations, not about end products. So the end product should be easy to vary, if you want to. But it should be hard to vary in the sense that you don’t want to.
Explanations are functions. In other words, explanations are software. There’s no sharp distinction between explanations and end products here. So the concern about tight coupling still applies.