Do Deutsch and Popper Disagree Over Refutation?

In my last post, I went over Popper’s own argument for why an asymmetry between refutation and verification exists. To summarize Popper’s view: Universal statements are more powerful than existential statements and thus of more interest to scientists. Since universal statements in logic can only be refuted, it makes sense that scientists will be more interested in falsifications than verifications. (Though scientists are interested in verifications, particularly as verifications of an experiment’s failure to refute a theory, i.e. corroborations. See also this post for discussion.)

But now that I was aware of why Popper preferred the language of refutation over the language of verification–due to the logical asymmetry that exists between the power of universal statements compared to the power of existential statements–I was left with a new problem. Consider this (full) quote from Deutsch in “The Logic of Experimental Tests”:

The asymmetry between refutation (tentative) and support (non-existent) in scientific methodology is better understood in this way, by regarding theories as explanations, than through Popper’s (op. cit.) own argument from the logic of predictions, appealing to what has been called the ‘arrow of modus ponens’. Scientific theories are only approximately modeled as propositions, but they are precisely explanations.

The Logic of Experimental Tests, P. 8 (Emphasis mine)

But wait! According to Popper, it is precisely because it is always possible to put theories into logical propositions that is the reason why there is an asymmetry between refutation and support. Absent this idea, it is not clear that there is an asymmetry between refutation and support.

Deutsch goes on to give his own reasons for why he feels there is an asymmetry:

An important consequence of this explanatory conception of science is that experimental results consistent with a theory T do not constitute support for T [1]. That is because they are merely explicanda. A new explicandum may make a theory more problematic, but it can never solve existing problems involving a theory (except by making rival theories problematic – see Section 3). [He then goes on to say the quote above] The asymmetry between refutation (tentative) and support (non-existent) in scientific methodology is better understood in this way…

The Logic of Experimental Tests, P. 8 (Emphasis mine)

So to Deutsch, the reason for the asymmetry between refutation and support isn’t about the logic of the situation–a key part of Popper’s reasoning for why his epistemology works as a form of deductive logic!–but instead about why a new explicandum can’t solve any existing problem involving a theory. The two men’s reasoning seems different here.

Also note how Deutsch claims experiments that match the outcome of a theory do not support it. But recall this quote from Popper in my previous post here:

…It should be noted that a positive decision [in a test] can only temporarily support the theory, for subsequent negative decisons [in future tests] may always overthrow it. So long as theory withstands detailed and severe tests… we may say that… it is ‘corrobarated

LoSD, p. 10 (Italicized emphasis is Popper’s. Underlined is mine.)

Here we have Popper clearly using ‘corroboration’ and ‘support’ as synonyms!

So even Popper’s and Deutsch’s use of language is different because Popper is comfortable with calling successful tests ‘verified’ (as discussed here) and referring to corroboration as a kind of ‘support’ (as discussed here) or (for a short while) ‘confirmation’ whereas Deutsch seems less comfortable with such language.

Why Popper Cared So Much About Logic

This apparent difference solves another mystery. Why Popper seemed almost obsessed with putting things in terms of logic!

I had personally long bought into the Twit Rat idea that Popper’s “logicism” (I’m told that is actually an abuse of the term but that’s what I used to call it) was an unnecessary and pedantic way of looking at Popper’s epistemology. After all, explanations are only “approximately modeled as propositions, but they are precisely explanations.” Popper’s emphasis on logic seemed an unnecessary part of his epistemology right up until I realized that you can’t make sense of his emphasis on refutation over verification without understanding that scientific explanations can be modeled as logic and that logic itself dictates the reason why we prefer refutations over verifications. Absent that argument, there is no reason to prefer the language of refutation over the language of verification/support if we’re always doing refutations only within context of a theory-to-theory comparison.

So who is right here? I, at the time, saw no easy way to reconcile the two men on this point.

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