If anyone knows enough epistemology or philosophy of science, I'm wondering if there's an orthodox thing to say about explanations in cases like the following:
You're a hippie, lying on your back in a meadow where birds are fairly uncommon. You're carrying a drug that will cause you to have a visual hallucination of a flock of birds flying above you, but leave your reasoning abilities as normal. You take the drug, and soon enough, you have a visual experience as of a flock of birds flying above you. If you had experienced this without taking the drug, you would've believed that lots of birds really were flying overhead. But you know that you did take the drug.
I think it's pretty clear that in this case, it's rational to believe that there are no birds up there. Even though a causal story that implies the existence of birds would explain all the observational data, and even though you have no counterevidence against the birds' existence, you have no reason to accept the existence of the birds. All your observational data is already explained by something you have good reason to believe -- namely, that the drug has given you illusory bird sensations. If you have one good explanation of something, you don't keep buying other explanations and accepting them in conjunction with the first one. Maybe you accept an inclusive disjunction of them if other reasonable explanations are offered, but you don't jump to accepting the conjunction without further evidence.
So here's my question: What general principle of explanation do we appeal to in rejecting the real-birds explanation in the above case? One possibility is simplicity. You take on existential commitments in making explanations -- commitments to the existence of a causal mechanism by which the drug influenced your sensations, for instance. Occam's razor will slice away redundant existential commitments like a commitment to real birds.
I post this because I have a similar example in a paper, and I thought simplicity was doing the work, but Brian Leiter thought that was weird. If anyone has a better idea of what principles are involved here, I'd like to know!
You're a hippie, lying on your back in a meadow where birds are fairly uncommon. You're carrying a drug that will cause you to have a visual hallucination of a flock of birds flying above you, but leave your reasoning abilities as normal. You take the drug, and soon enough, you have a visual experience as of a flock of birds flying above you. If you had experienced this without taking the drug, you would've believed that lots of birds really were flying overhead. But you know that you did take the drug.
I think it's pretty clear that in this case, it's rational to believe that there are no birds up there. Even though a causal story that implies the existence of birds would explain all the observational data, and even though you have no counterevidence against the birds' existence, you have no reason to accept the existence of the birds. All your observational data is already explained by something you have good reason to believe -- namely, that the drug has given you illusory bird sensations. If you have one good explanation of something, you don't keep buying other explanations and accepting them in conjunction with the first one. Maybe you accept an inclusive disjunction of them if other reasonable explanations are offered, but you don't jump to accepting the conjunction without further evidence.
So here's my question: What general principle of explanation do we appeal to in rejecting the real-birds explanation in the above case? One possibility is simplicity. You take on existential commitments in making explanations -- commitments to the existence of a causal mechanism by which the drug influenced your sensations, for instance. Occam's razor will slice away redundant existential commitments like a commitment to real birds.
I post this because I have a similar example in a paper, and I thought simplicity was doing the work, but Brian Leiter thought that was weird. If anyone has a better idea of what principles are involved here, I'd like to know!