One of my favorite historical stories is that of miasma theory. It is also known as the theory that bad air causes disease. The scientific word “miasma” comes from ancient Greek and means “pollution.” More common usage adopted the medieval Italian word “malaria,” meaning “bad air.”
As you probably have already guessed, the disease malaria was once thought to be caused by bad air. That was the primary theory of disease going back to ancient times in both Europe and China. Ancient physicians Hippocrates and Galen bought into the miasma theory and the idea of preventing disease by preventing exposure to bad air was widespread throughout Europe until the late 1800s.
In the late 1800s, miasma theory was gradually replaced by germ theory. The latter was definitely an advance in medicine, but it wasn’t as if miasma theory was wrong-headed. It wasn’t like bloodletting—the bizarre notion that it would be helpful to bleed a patient already weakened by illness. The miasma theory was actually quite sensible, and still helpful today.
People are pretty good at noticing correlations between events. Philosopher David Hume argued that our beliefs that we call “knowledge” are habits we develop through continually noticing correlations. Correlation is not causation, but correlation is a leading cause of beliefs.
In the case of miasma, people continually noticed the correlation between disease and bad odors. They noticed that certain diseases were more common near swamps, like malaria. They noticed that disease was more frequent when there were more odors from rotting organic matter, like trash heaps and corpses. That’s the thinking behind the painting at the beginning of this article. Like many others, the artist was aware of the correlation that battles resulted in a large number of dead bodies which then resulted in an increase in cholera in the area. Then there was the correlation between people suffering from disease and bad smells emanating from them. This was especially the case for the much-feared bubonic plague.
The miasma theory of disease quite sensibly reasoned that if diseases like cholera, malaria, and plaque were caused by bad air, then the way to prevent and treat those diseases was to reduce or eliminate the bad air. That thinking led governments and health campaigners to drain swamps, clean up refuse in cities, and ensure that water supplies were free of odors.
People being good at noticing correlations, they noticed that taking these actions reduced both the bad smells and the level of disease. Correlation is not causation, but hey, it seemed to be working so they kept doing it. Technically, people were incorrect that it was the removal of bad air was preventing disease, but their wrong belief was useful and saved countless lives.
So Why Am I Talking About This?
Am I advocating believing in wrong ideas? No, I am discouraging hubris. People are prone to think they are more knowledgeable than they are. The reality is that what we believe we know is, as Hume pointed out, more a result of habit than knowledge. People who believe in science are frequent offenders, smugly believing they are so much smarter than people in the past who believed in theories that are now out of favor.
Maybe we now understand certain things better than people did in the past. That doesn’t mean that those people in the past were less intelligent or even ignorant. Most of what we “know” today will be supplanted by other theories in the future. That’s how it works, both science and ordinary life. All people, in all eras, past present and future, are trying to make sense of the world by noticing correlations and responding accordingly.
Friedrich Nietzsche wrote, in his typical crusty style, that sometimes wrong beliefs can still be valuable. The pragmatist philosophers argued that what makes an idea true is its usefulness. Few ideas are more useful than that foundational tenet of pragmatism. We are all just theorists responding with beliefs to the correlations we think that we see in the world. Hubris, the pretentious attitude that you know so much, is the enemy of learning and understanding. Miasma theory is strong evidence for that being humble and open-mindedly observing the world is a life strategy much more useful than dogmatism.