I’m a strong believer in modus ponens, in any domain of discourse where I know the meanings of all the words!
Scott Aaronson in reply to Max Tegmark replying to Scott's review of Max's book. He goes on:
In physics, however, I only believe in “approximate modus ponens,” in the following sense: if I accept “A” and “A⇒B,” then I’ll tentatively accept “B,” but I might decide on further reflection that I meant something different by a word appearing in “B” than by the same word in “A” or “A⇒B.” And in any case, I rarely would’ve considered “A” or “A⇒B” certain, just very well-established. For both of those reasons, I can start with physics statements that I consider to be well-established, apply enough steps of “modus ponens,” and end with a statement I consider to be speculation!
(Emphasis mine.)
This sounds similar to the view that is sometimes called the fragility of deduction. It was why John Stuart Mill distrusted "long chains of logical reasoning" and according to Paul Samuelson it is why "Marshall treated such chains as if their truth content was subject to radioactive decay and leakage."
Another month has passed and here is a new rationality quotes thread. The usual rules are: