Doug, I have not yet gotten to any position on the main issue here, but I think your comparison won't do either to image or structure an argument.
The point would seem to be, not whether ghosts and witches existed, but whether (provisionally assuming their existence, i.e. the authenticity of "witchology," Shakespeare in his uses of witches and ghosts showed an understanding of that "ology." I would argue (a) that he did in fact show such a deep understanding, and (b) that had he not had such an understanding his use of witches and ghosts would have been a defect in his poetry. (In fact, what we seem to *mean* by Shakespeare is someone who by definition would not make such a mistake -- in context after context.)
Two hundred years later Shelley (who did not believe in ghosts and did believe in chemistry) was equally careful to understand accurately both the principles of chemistry and the principles of the (dead) "science" of invoking spirits of the dead. Any inaccuracy in the latter would cripple *Ode to the West Wind*. And incidentally, the most famous factual error in the history of English literature, Keats's Cortez looking at the Pacific, was probably *not* an inaccuracy but a precision: the whole poem revolves around seeing, personally for the first time, something that *others* (e.g., Balboa, etc) had ALREADY seen. Critics always assume that proletarian poets (those who can take the dimunitives "Johnny" or "Bobby") are ignorant.
In reference to poetry at least, I think Brad is correct and you are wrong. I'm currently taking up the reading of late 20th c. fiction which I dropped back in '65 when I got involved in politics. Chemistry permeates Pynchon's *Gravity's Rainbow* which I'm about 80% through, and I would strongly suspect (though my knowledge of chemistry is too insignificant for me to judge) that Pynchon's chemistry in that novel is accurate, and that any inaccuracies are deliberate and controlled.
Carrol