There's scientific knowledge. There are the dedicated scientists who make it, whether laboring in laboratories or in the fields, fretting over data analysis, refereeing each other's manuscripts or second-guessing themselves.

And, well, there are some crackpots.

I'm not talking dancing-on-the-edge-of-the-paradigm folks, nor cheaters who seem to be on a quest for fame or profit. I mean the guy who has the wild idea for revolutionizing field X that actually is completely disconnected from reality.

Generally, you don't find too much crackpottery in the scientific literature, at least not when peer review is working as it's meant to. The referees tend to weed it out. Perhaps, as has been suggested by some critics of peer review, referees also weed out cutting edge stuff because it's just so new and hard to fit into the stodgy old referees' picture of what counts as well-supported by the evidence, or consistent with our best theories, or plausible. That may just be the price of doing business. One hopes that, eventually, the truth will out.

But where you do see a higher proportion of crackpottery, aside from certain preprint repositories, is at meetings. And there, face to face with the crackpot, the gate-keepers may behave quite differently than they would in an anonymous referee's report.

Doctor Crackpot gives a talk intended to show his brilliant new solution to a nagging problem with an otherwise pretty well established theoretical approach. Jaws drop as the presentation proceeds. Then, finally, as Doctor Crackpot is aglow with the excitement of having broken the wonderful news to his people, he entertains questions.

Crickets chirp. Members of the audience look at each other nervously.

Doctor Hardass, who has been asking tough questions of presenters all day, tentatively asks a question about the mathematics of this crackpot "solution". The other scholars in attendance inwardly cheer, thinking, "In about 10 seconds Doctor Hardass will have demonstrated to Doctor Crackpot that this could never work! Then Doctor Crackpot will back away from this ledge and reconsider!"

Ten minutes later, Doctor Crackpot is still writing equations on the board, and Doctor Hardass has been reduced to saying, "Uh huh …" Scholars start sneaking out as the chirping of the crickets competes with the squeaking of the chalk.

Granted, no one wants to hurt Doctor Crackpot's feelings. If it's a small enough meeting, you all probably had lunch with him, maybe even drinks the night before. He seems like a nice guy. He doesn't seem dangerously disconnected from reality in his everyday interactions, just dangerously disconnected from reality in the neighborhood of this particular scientific question. And, as he's been toiling in obscurity at a little backwater institution, he's obviously lonely for scientific company and conversation. So, calling him out as a crackpot seems kind of mean.

But ... it's also a little mean not to call him out. It can feel like you're letting him wander through the scientific community with the equivalent of spinach in his teeth while trailing toilet paper from his shoe if you leave him with the impression that his revolutionary idea has any merit. Someone has to set this guy straight ... right? If you don't, won't he keep trying to sell this crackpot idea at future meetings?

For what it's worth, as someone who attends philosophy conferences as well as scientific ones (plus an interesting assortment of interdisciplinary conferences of various sorts), I can attest that there is the occasional crackpot presentation from a philosopher. However, the push-back from the philosophers during the Q&A seemed much more vigorous, and seemed also to reflect a commitment that the crackpot presenter could be led back to reality if only he would listen to the reasoned arguments presented to him by the audience.

In theory, you'd expect to see the same kind of commitment among scientists: if we can agree upon the empirical evidence and seriously consider each other's arguments about the right theoretical framework in which to interpret it, we should all end up with something like agreement on our account of the world. Using the same sorts of knowledge-building strategies, the same standards of evidence, the same logical machinery, we should be able to build knowledge about the world that holds up against tests to which others subject it -- and, we should welcome that testing, since the point of all this knowledge-building is not to win the argument but to build an account that gets the world right.

In theory, the scientific norms of universalism and organized skepticism would ensure that all scientific ideas (including the ones that are en face crackpot ideas) get a fair hearing, but that this "fair hearing" include rigorous criticism to sort out the ideas worthy of further attention. (These norms would also remind scientists that any member of the scientific community has the potential to be the source of a fruitful idea, or of a crackpot idea.)

In practice, though, scientists pick their battles, just like everyone else. If your first ten-minute attempt at reaching a fellow scientist with rigorous criticism shows no signs of succeeding, you might just decide it's too big a job to tackle before lunch. If repeated engagements with a fellow scientist suggest that he seems not to comprehend the arguments against his pet theory -- and maybe that he doesn't fully grok how the rest of the community understands the standards and strategies for scientific knowledge-building -- you may have to make a calculation about whether bringing him back to the fold is a better use of your time and effort than, say, putting more time into your own research, or offering critiques to scientists who seem to understand them and take them seriously.

This is a sensible way to get through a day which seems to have too few hours for all the scientific knowledge-building there is to do, but it might have an impact on whether the scientific community functions in the way that best supports the knowledge-building project.

In the continuum of "scientific knowledge", on whose behalf scientists are sworn to uphold standards and keep out the dross, where do meetings fall? Do the scientists in attendance have any ethical duty to give their candid assessments of crackpottery to the crackpots? Or is it OK to just snicker about it at the bar? If there's no obligation to call the crackpot out, does that undermine the value of meetings as sources of scientific knowledge, or of the scientific communications needed to build scientific knowledge?

Could a rational decision not to engage with crackpots in one's scientific community (because the return on the effort invested is likely to be low) morph into avoidance of other scientists with weird ideas that actually have something to them? Could it lead to avoidance of serious engagement with scientists one thinks are mistaken when it might take serious effort to spell out the nature of the mistakes?

And is there any obligation from the scientific community either to accept the crackpots as fully part of the community (meaning that their ideas and their critiques of the ideas of other ought to be taken seriously), or else to be honest with them that, while they may subscribe to the same journals and come to the same meetings, the crackpots are Not Our Kind, Dear?