I guess I disagree that the premise “D is the best explanation for ~K” needs to be explicitly said or expressed in order to interpret her reasoning as an IBE. I think that people make IBEs all the time while never explicitly thinking to themselves that H is the best explanation for E. Compare a rule like Modus Ponens–you can (or perhaps do) reason in accordance with MP without using it as a premise. I think it’s natural to see IBE the same way, as a kind of inference rule. But regardless, premises in everyday reasoning are often elided.

I’m also not sure I see why if she made the IBE she would rather say “I’m probably in a dream”. If ~K makes D probable (above say, some threshold), then it’s very natural to believe D and hence be in a position to assert it. And at any rate IBEs, while inductive arguments, need not be probabilistic or only support probabilistic judgments. Enumerative inductive arguments, for example, license unqualified universal claims.

I grant that my background views about logic and reasoning may be clouding my judgment, but I don’t see that it’s clearly a deductive conditional argument. Something I think supports this is that independent of any particular interpretation of what’s going on, I take it that she has good reason to believe she’s in the dream, based on their conversation and the context. Given what she knows about DiCaprio and the dream sharing, the fact that she cannot remember how she got there is good reason to think she’s in the dream. So the question is whether she comes to believe she’s in a dream irrationally by affirming the consequent and hence does not justifiably believe she’s in the dream, or whether her belief is justified. I acknowledge my use of a bit of the principle of charity in assuming the latter. The rational inference is there and easy for the taking, and I see more reason than not to assume she takes it. With just this small scene in front of us it’s hard to see precisely on what reasons she’s based her belief. (And I think this may be the kernel of our disagreement.) We’d have to ask her what her reasons are. I just don’t see her responding “Well, ~K, and because D -> ~K, it must be that D” while not also saying something like “and also because DiCaprio can create dreams that look similar to this” etc.

Anyway, I don’t want to say that using this clip to illustrate consequent affirming is not a useful exercise for students–DiCaprio doesn’t actually assert the English conditional (he says “You never remember the beginning of your dreams, do you?”) and it’s very good practice to uncover the logic of the conversation, and a good way to raise the issue of consequent affirming, which is important. Thanks for the example and I’ll bookmark the clip to use it in my classes! And thanks for pushing back–it’s helped me understand stuff better.