As you certainly know, Rabbi Nosson Slifkin is in hot water because he said that the Sages of the Mishna and Talmud (Chazal) might have been wrong about the natural world. (Well, actually, prominent Rishonim and Achronim, chas v'sholom, said it first, but no modern day "Godol" is going to put them in hot water.)
Anyway, in his Mysterious Creatures, an interesting book with a bad cover and a horrible font, R. Slifkin says that the mistakes Chazal seem to have made about science can fall into five categories. Briefly they are:
(1) Nes Chazal were right, but over the last 2000 years nature has changed
(2) Nisayon Chazal were right, and you can't trust those atheist scientist who are just lying to you for the purpose of furthering their secular aganda
(3) Metaphor When Chazal appeared to be speaking about science they were, in fact, speaking in a sort of code, and their real subject wasn't science but metaphysics or morality or something else.
(4) Misunderstanding In a living language, the meaning of words change over time, so when Chazal, for example, said "dragon" they really meant snake; and
(5) Mistake Chazal were just wrong. They were experts in halacha, not science, so they relied on the folk wisdom of their day and, in some cases, made mistakes.
Ok, with me so far? Good. Let's go one step further.
If we can say that Chazal were wrong about the natural world, because they occasionally relied on the folk wisdom of their time (that's plain and clear from the writings of Rabbenu Avraham, btw) why can't we say the same thing about the Achronim? (later authorities)
For example, every 17th century bubbushka beleived in demons and gilguls, right? So why should it mean anything if some achronim did, too?
