From Kwame Anthony Appiah's Cosmopolitanism: Ethics in a World of Strangers:

There’s an oft-told anecdote about a medical missionary in a remote place, who watches, in horror, as people give untreated well water to their babies. The children regularly get diarrhea, and many of them die. The missionary explains that, even though the water looks clear, there are tiny, invisible creatures in it that make the children sick. Fortunately, she says, if they boil the water, it will kill these bacteria. A month later she’s back, and they’re still giving the babies the dirty water. After all, if a stranger came into your community and told you that your children got influenza because of witchcraft, would you respond by going out and slaughtering a sheep? Then the missionary has another idea. Look, she says, let me show you something. She takes some water and boils it. See, she says, there are spirits in the water, and when you put it on the fire they flee: those bubbles you see are the spirits escaping, the spirits that are making your children sick. Now boiling water makes sense. Now the babies stop dying. In belief, as in everything else, each of us must start from where we are.

When people get sick for unaccountable reasons in Manhattan, there is much talk of viruses and bacteria. Since doctors do not claim to be able to do much about most viruses, they do not put much effort into identifying them. Nor will the course of a viral infection be much changed by a visit to the doctor. In short, most appeals in everyday life to viruses are like most everyday appeals to witchcraft. They are supported only by a general conviction that sickness can be explained, and the conviction that viruses can make you sick.

If you ask most people in Manhattan why they believe in viruses, they will say two kinds of things: First, they will appeal to authority. “Science has shown,” they will say, though if you ask them how science showed it, you will pretty quickly reach an impasse (even with scientists, by the way, unless they happen to be virologists unusually curious about the history of medicine). Second, they will point to phenomena—the spread of HIV or the common cold, the death of their great-aunt last winter, a picture of a virus they once saw in a magazine—where the viral theory explains what happened.

Similarly, in Kumasi, people who are asked why they believe in witchcraft will appeal to authority, too. “Our ancestors taught us about it.” And they will then go on to tell you of cases of witchcraft they have seen or heard of, filling in for you all the things that it explains. Sir Edward Evans-Pritchard, one of the greatest anthropologists of the twentieth century, wrote a wonderful book called Witchcraft, Oracles and Magic among the Azande, about a people of that name who live in the Sudan. Having explained their ideas about witchcraft in great detail, he observes at one point that sometimes, in the evenings, when he saw a flash of flame in the bush around the Azande settlement where he was living, he found himself thinking, “Look, a witch.” Of course, he didn’t believe it, really. He knew it was probably someone from the village going off to relieve himself, carrying a flaming torch to guide him on his way. But what he was teaching us is that what you see depends on what you believe. What it’s reasonable for you to think, faced with a particular experience, depends on what ideas you already have.

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The slow invention of better metaphors over the past few centuries may be enough to explain the Flynn Effect.

I'm not sure what you find interesting about the quote but I think it's pretty badly mistaken in trying to make it look like belief in witchcraft is very similar to belief in viruses.

 

When people get sick for unaccountable reasons in Manhattan, there is much talk of viruses and bacteria. Since doctors do not claim to be able to do much about most viruses, they do not put much effort into identifying them. Nor will the course of a viral infection be much changed by a visit to the doctor. In short, most appeals in everyday life to viruses are like most everyday appeals to witchcraft. They are supported only by a general conviction that sickness can be explained, and the conviction that viruses can make you sick.

Two things look wrong to me here:

  • It's pretty important to distinguish bacterial infections (for which there can be effective treatment) from viral infections (where I think often there is no treatment). (I'm pretty sure witchcraft theory of sickness can't tell the difference very well) (also vaccines are a things and work against some viruses, AFAIK witchcraft doesn't have anything similar)
  • If you suspect you have a viral infection and you care to avoid infecting others you can take an effective preventive measures. Not sure if witchcraft theory of sickness could help you.

If you ask most people in Manhattan why they believe in viruses, they will say two kinds of things: First, they will appeal to authority. “Science has shown,” they will say, though if you ask them how science showed it, you will pretty quickly reach an impasse

I'm not in Manhattan so I'm not sure if is counts. (I'm also not a virologist) But it should be relatively easy to design experiments to demonstrate that some diseases are transmitted by replicating things. First check if you can infect one subject with (a thing like a bit of snot) from a sick subject. Then try infect a bunch of subjects with diluted (thing like a bit of snot) to check how much you can lower the dose before it stops being infectious. Then take (a thing like a bit of snot) that received ~minumum infective dose, dilute it a bit (so if it was a non-replicating thing like poison dose would be too low to cause symptoms), infect some more subjects & you're done.

(actually running this would be probably pretty hard)

This gets you only that a replicating thing is causing the infection. To check that it's a virus... well you need a really good microscope so you can identify all the really small things, something to let you separate them and check which kind of the small thing is causing infection.

(also as far as I can tell this is asking much less from witchcraft; I'm not sure if witchcraft can tell difference between poisoning, bacterial infection, parasite infection, viral infection, vitamin deficiency, ....) (some of those are much easier to distinguish and treat than many viral infections)

trying to make it look like belief in witchcraft is very similar to belief in viruses.

I feel like you're missing the point. Of course, the germ theory of disease is superior to 'witchcraft.' However, in the average person's use of the term 'virus,' the understanding of what is actually going on is almost as shallow as 'witchcraft.' Of course, 'virus' does point towards a much deeper and important scientific understanding of what is going on, but in its every day use, it serves the same role as 'witchcraft.'

The point of the quote is that sometimes, when you want to get a message across (like 'boil the water before drinking it') it's easier to put yourself into the other person's ontology and get the message across in terms that they would understand, rather than trying to explain all of science.

Yes, I felt that I was missing a point, thank you for pointing to the thing you found interesting in it.

it's easier to put yourself into the other person's ontology and get the message across in terms that they would understand, rather than trying to explain all of science.

Is a thing that makes sense. But I think the quote doesn't point at it very well. First a big chunk of it is asserting that belief in witchcraft theory of disease is similar to belief in germ theory of disease. (I don't know how well average person understands what are viruses)

Second where it talks about convincing by making concepts similar it's weird. For example

... people give untreated well water to their babies. The children regularly get diarrhea, and many of them die  (...) if they boil the water, it will kill these bacteria. A month later she’s back, and they’re still giving the babies the dirty water. After all, if a stranger came into your community and told you that your children got influenza because of witchcraft, would you respond by going out and slaughtering a sheep?

Influenza is much smaller risk than cholera (quick search says CFR for untreated cholera 25-50%, for flu 0.1%) and boiling water is much less costly than slaughtering sheep (it's likely to result in prison time where I live). (EDIT to add: I didn't check those numbers so don't trust them too much, they're just first numbers I could find and they roughly match my expectations)

Again thanks for explaining. (at least for me) your comment made the point much better than the quote in the post.

It's also an interesting example of where consequentialist and Kantian ethics would diverge.

The consequentialist would argue that it's perfectly reasonable to lie (according to your understanding of reality) if it reduces the numbers of infants dying and suffering. Kant, as far as I understand, would argue that lying is unacceptable, even in such clear-cut circumstances.

Perhaps a Kantian would say that the consequentialist is actually increasing suffering by playing along with and encouraging a system of belief they know to be false. They may reduce infant mortality in the near-term, but the culture might feel vindicated in their beliefs and proceed to kill more suspected "witches" to speed up the process of healing children.