Dr. Seward, the narrator of a large part of Dracula, sometimes seems like he’s there to make the reader feel relatively intelligent. His inability or unwillingness to comprehend things outside his experienced make him, despite his self-avowed erudition, the last person to understand what’s going on.
Dr. Seward refers to himself as a “sceptic” four times over the course of the novel. Old Pyrrho being unavailable, I’ll step in to say that’s not really what he is. Skeptics don’t believe absolute knowledge is possible, and that includes their own preconceptions. Seward has a solid base of things he knows, and anything contradicting it gets disregarded. Skeptics doubt their own working assumptions and even the framework in which they reason, the same as new information they receive. Dr. Seward isn’t doing that at all. In terms of Bayesian logic, he’s reasserting strong prior probabilities in the face of evidence to the contrary. There’s a word for that: the economist Noah Smith calls it “derp”.
Wait – what’s a “prior probability”? Bayes’s theorem is one of those amazing mathematical results that sits there for centuries before anyone really gets its significance. The basic idea (and you can look to Dr. Smith’s blogpost for a better explanation than mine) is that every thinker has a certain prior base of knowledge that she uses to interpret new information. As new information comes in, it modifies the odds of each thing in the base, leaving the thinker with a new “prior distribution” of (in this case) the likelihood that each possible cause gives rise to future observed effects. The mathematical operation that makes that happen is multiplication. One immediate result, therefore, is that if your prior distribution says the likelihood that thing X caused event Y is exactly zero, then the new information gets multiplied by zero. There’s no amount of new data that can make you think X is really going on. Dr. Seward has a prior distribution with zeroes assigned to everything he didn’t learn in school. A skeptic uses a prior distribution with no zeroes in it at all (like a bell curve), because those zeroes are awesomely powerful things, and they’re not to be trusted.
Perhaps I’m being too hard on the good Doctor, but I feel justified because there are examples right next to him of better ways to reason. Characters who use prior probabilities derived from literature seem to work much better. Mina Harker, for example; at times she seems to be the brains of the whole outfit. Why do I say her priors come from literature? Mina may have taken Corey Olsen’s Faërie and Fantasy class (or the 19th-century equivalent). She knows how to compose an oath so it doesn’t later cause trouble in an entirely-predictable way. Maybe this is why Prof. Olsen says she’s “awesome”. Mina reasons from stories. Here’s how she swears never to read her husband’s diary: “I would never open it unless it were for his own dear sake or for the sake of some stern duty.” (Chapter IX) When I read that, I said, “Brava!”  She drew the crucial lesson from Arthurian romances – be really careful how you swear oaths. That “unless” clause made the happy ending possible. (Oops – spoiler!) The sons of Fëanor should have been so wise.
Jonathan Harker has a similar skill at hedging his oaths, though I’m sure his prior probabilities come from law school. On the expedition to Dracula’s castle, Mina tries to make him understand that her life is secondary in importance to ridding the world of vampires. “’Jonathan, I want you to promise me something on your word of honour. A promise made to me, but made holily in God’s hearing, and not to be broken though I should go down on my knees and implore you with bitter tears. Quick, you must make it to me at once.’
“’Mina,’ I said, ‘a promise like that, I cannot make at once. I may have no right to make it.’” (Chapter XXIV) You have to love that “may have” — he won’t even commit to that, without consulting his books of precedents. Any knight of the Round Table would have sworn instantly and suffered for it for the rest of the poem.
The similarity of Mina’s and Jonathan’s thought processes raises a question. Instead of school, did Mina learn this mode of thought after meeting Jonathan, to be a better wife? Doing such a thing would be consistent with her character, since it’s not much more difficult than memorizing Transylvanian railroad schedules without speaking Romanian. But I prefer to think that it’s the way she was educated. Victorian girls were taught by literary example (I admit it: my own prior probability distribution is influenced most heavily by Alice’s Adventures in Wonderland). I’m sure that a mode of thinking so consistent with the British legal system was one of the salutary qualities that attracted Jonathan to her in the first place.
 Some people write in the margins of books. I talk to them.[back]