What is the difference between revising a theory and creating an ad hoc explanation to save your theory? Furthermore, at what point is one forced to give up their original theory because it conflicts too greatly with new data? In other words, when does a theory suffer "death by a thousand qualifications"? I realize that there is a difference because theory revision is an important part of philosophy and science, but I'm having trouble communicating a relevant difference.

To add some further context: I started thinking about this question because I was thinking about an atheist objection I've heard to arguments for theism. Essentially, the atheist claims that theists can't be argued with because anytime they bring evidence against their position, the theists qualify their position.

My anticipated response to this objection was that if the theist is guilty of this, then so is everybody in philosophy and science. Philosophers and scientists constantly revise and qualify their theories, arguments, and positions to strengthen them. However, this response did make me wonder how we would differ theory revision from simply being ad hoc.

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    According to some points of view a "good" theory revision is a modification of the theory that adds content, while "bad" ad hoc is only limited to avoid an experimental refutation. May 18, 2020 at 15:28
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    Excellent question. In some cases, there's no distinction at all. "A scientific truth does not triumph by convincing its opponents and making them see the light, but rather because its opponents eventually die and a new generation grows up that is familiar with it." Quotation by Max Planck. Historically speaking, scientific theories reach the breaking point after lots of ad hoc modification, and in light of new evidence. There are still PhDs trying to disprove evolution.
    – J D
    May 18, 2020 at 17:40
  • After you learn about greatly simplified reasoning like deductive and inductive reasoning, read up on defeasible reasoning. Informal logic is a highly domain-centric practice, as Toulmin pointed out in his Uses of Argument, and coincides with predominant thinking about indeterminancy in physical science.
    – J D
    May 18, 2020 at 17:45
  • Lastly, underdetermination which has reared it's head since Quine, also goes to show that theories, which are constructs of minds, are limited representations of reality, and that what constitutes reality exactly is hard to nail down. Hence theories are amenable to both modifcation and revision, because there's a certain amount of uncertainty inherent in measurement, logical consistency, and correspondence between the state of affairs in the world and our subjective experience of them.
    – J D
    May 18, 2020 at 17:48
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    Popper, Lakatos, Kuhn, Feyerabend (see related entries into SEP). May 19, 2020 at 5:58

1 Answer 1


Karl Popper taught us the importance of looking for refutations. Any view worth believing in, MAKES PREDICTIONS, and can be refuted. His early thinking about this process needed revision, as it treated refutations as individually decisive. However, because theory is underdetermined by evidence, EVERY theory can be patched to address any evidence. Therefore, one needs an additional criteria to evaluate when accumulating patches make a theory effectively refuted.

Popper's solution was to reformulate Occam's Razor in terms of predictive power. When modifications to patch a theory produce no predictive power, they are pure desperation patching. If the major tests of a theory all call for pure patches -- it is probably time to toss it. This is, of course, a subjective judgement, which all Occam tests are. But it is at least less of a pure judgement than "simplicity" is.

Lakatos came up with a better version of Popper's falsificationism, with his progressive vs. regressive research programme: http://people.loyno.edu/~folse/Lakatos.html Lakatos approach seems to describe well, how science ought to be done. It too, calls for judgement.

The other recent idea which has a bearing is consilience, which is explained here: http://warincontext.org/2014/01/28/the-importance-of-consilience-in-science/

Discussions between theists and atheists often feature a lot of ad hoc patches. Both parties generally are unmoved by their patches being pointed out, because they each think there is a consilience of evidences supporting their research programme, and it offers enough value in living life that it is progressive despite the occasional need for ad hoc patches. They both also generally presume that they can find better patches soon that will be less ad hoc, so even temporary apparent regressivity is just a "bad patch".

It is very difficult for someone to do an honest evaluation of a worldview they hold by. One can try to total up the negatives and positives, and try to figure out if it is progresssive or regressive, but the answer will almost always be "progressive" by using weighting of different issues differently. But -- for someone experiencing a set of negative evidences -- there often is an unconscious realization that one's worldview is under justifiable threat. Those who abandon/deconvert from a worldview, generally do so because an accumulation of issues just became to stressful to them. This is -- a consilience of evidences forcing the realization that the programme is regressive!

I hope this answer is helpful.

  • Thank you, this helped to clarify the issue! May 24, 2020 at 3:25

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