Bold Vs Ad Hoc Theories

I previously have quoted Popper on why we must not use ad hoc theories to save a theory. Popper addresses this multiple times in his writings because if we do not accept, as a methodological rule, that we will not save our theories via ad hoc explanations that every theory becomes (to use the Deutsch term) ‘easy-to-vary’. In other words, ad hoc explanations attached to a theory make it impossible to falsify. This is because a theory that can be falsified is ‘bold’ and takes chances and a theory that is saved by ad hoc theories is not.

[When speaking of] ‘the best theory’ it is assumed that a good theory is not ad hoc. The idea of adhocness and its opposite, which may perhaps be termed ‘boldness’, are very important. Ad hoc explanations are explanations which are not independently testable; independently, that is, of the effect to be explained. They can be had for the asking, and are therefore of little theoretical interest.

Objective Knowledge, p. 15-16 (Italicized emphasis is Popper’s. Underlined is mine.)

Popper makes this even more clear here:

…it is… impossible… that any theoretical system shouldever be conclusively falsified. For it is always possible to find some way of evading falsification, for example by introducing ad hoc an auxilary hypothesis, or by changing ad hoc a definition. It is even possible without logical inconsistency to adpot the position of simply refusing to acknowledge any falsifying experience whatsoever. … I must admit the justice of this criticims. …I am going to propose… that the ’empirical method shall be characterized as a method that excludes preicsely those ways of evading falsification

LoSD, p. 19-20

Let me put this somewhat more bluntly, Popper’s epistemology with ad hoc explanations is exactly equivalent to not doing Popper’s epistemology at all. Thus “Popperians” that freely utilize ad hoc explanations or saves are exactly equivalent to not being Popperian at all. So this is not a small point. It’s the difference between following and not following Popper’s epistemology. See this post for discussion and an example.

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