The Semmelweis Reflex

by Captain Walker

Categories: Psychology & Philosophy, Science & Medicine, CW

For quite some time I’ve been thinking that there must be a term to describe something I was observing over the last 25 years. Then I finally found it by accident today! This is not a lecture – just in case.  I found it in Bo Bennett’s book ‘Uncomfortable Ideas‘.


The Semmelweis reflex is a metaphor for the reflex-like tendency to reject new evidence or new knowledge because it contradicts established norms, beliefs, or paradigms.

This will not be unpacked further – use a dictionary!


Eating unusual things: I like to try unusual foods – or what I think might be food. So for example I’ve tried frogs legs, crocodile, ostrich, opossum, horse meat. I’ve not had the opportunity to try rats (carefully reared). I have tried locust on one occasion. The interesting thing was that when over the years I’ve mentioned to others some of my food-adventures, I invariably got twisted faces with people going “Stop! Stop! I don’t want to vomit – I can’t think about it!” Calm down! I wasn’t trying to get anyone else to try that lot. The point is there was a reflex action to reject the mere idea of it. Chicken or beef is fine for some. If you’ve been grown up as a muslim then pork is automatically rejected, and I’m not going into why. If all your life you have been a vegetarian, meat is automatically ‘no go’ for contemplation. Caution: I did not say or imply that people ‘have to eat meat’!

It’s not just about food. If I had conversations with religionists and I said, “Would you consider for the moment that there may actually be no God?” Of course, those people were trying to convert me from atheism. Well, their answer would be a straight “No! I wouldn’t consider that.” – one of the few times I got a straight answer. To the God believer the reflex is to reject the thought pretty instantly. Their norm or belief system can’t tolerate the thought of life without a God. Ahhh.. but as an atheist, I’m meant to be attentive? No. I would listen to religionists, because I’m usually interested in an alternative point of view. I’m not worried if perchance they would convert me – not that I’m overconfident. I would really like to see a different perspective and I’m open to changing my mind.

What it means to me

I’m not saying that people ought to try jumping off a cliff or using cocaine for new experiences! There are some things that are dangerous to life and health. Pork or beef or carefully reared rat meat, isn’t dangerous to life. So doing the cocaine thing is different to thinking about trying rat-burger.

Sometimes there is evidence of an association between two things that is very powerful. Causation may be hidden. This is how the Semmelweis reflex became recognised.

From Wikipedia

Ignaz Semmelweis discovered in 1847 that hand-washing with a solution of chlorinated lime reduced the incidence of fatal childbed fever tenfold in maternity institutions. However, the reaction of his contemporaries was not positive; his subsequent mental disintegration led to him being confined to an insane asylum, where he died in 1865.

Semmelweis’s critics claimed his findings lacked scientific reasoning. The failure of the nineteenth-century scientific community to recognize Semmelweis’s findings, and the nature of the flawed critiques outlined below, helped advance a positivist epistemology, leading to the emergence of evidence-based medicine.

To learn more of the culture of medical practice that Semmelweis encountered in the 1850’s – which resembles what I know in the last 1o years – read stuff at PBS.

Back then, they did not have a good understanding of how ‘bugs’ operated to pass infections. Today all this seems pretty basic and second-nature.

I recall back round 1984 when a certain physician in a third-world country had prescribed antibiotics to patients with ‘stomach ulcers’. He said that he had good results that were unpublished. I thought he was barking mad! I rejected the idea out of hand, with that sort of reflex action. Well, many years later helicobacter pylori (a bug) as found, that had a real causal role in some ‘stomach ulcers’ (I’m using the term loosely here). Then it became known that antibiotics can actually cure a good proportion of those people. I recall thinking how stupid I was in 1984. It’s not that I didn’t know or could not have imagined. It was because I did not investigate further.

The emergence of COVID-19 is another one. People instantly reject the idea that it could have been designed as a bioweapon. They don’t have time to evaluate the evidence for that. Instead they’d bark “Conspiracy theorist!” And in the last couple days a US Intelligence report has cast doubt on the bioweapon theory. People who don’t want to dig deeper will simply accept the headline and move on. So – Semmelweis was in a similar situation – he had the chains of evidence pointing to some causative mechanism or actual cause, but he couldn’t put his finger on it. In the COVID-19 situation the evidence is missing because China removed key parts of it. But there are other sound bits of evidence that leave a causative trail.

Comparison of three concepts


  1. When something pretty crazy happens or presents itself, I’d be more cautious in rejecting it or explanations for it.
  2. Not everybody is a conspiracy theorist.
  3. Some conspiracy theories may lack solid evidence but there may be an evidential trail that’s not visible to others.
  4. Carl Sagan led the way on the true nature of science.
  5. People of science need to be more cautious.

Disclaimer & Guidance

The reading of posts on this blog is subject to the Terms & Conditions. Unpalatable truths and personal experiences may be told. Nothing posted on this blog is directed at any identified person. On occasions individuals are quoted anonymously. That does not mean that they have been identified to the world. Should any person or organisation reading this blog find something that makes them feel or know that they  are being referred to – any such perceived identification does not mean ‘identified to the world’. ‘Stupid‘ is an impish figment of my imagination who occasionally is allowed to pop up – and does not represent any known individual, individuals or groups. The treatment of  ‘Stupid‘ is not representative of the way people are treated in real life. Adverse inferences made are dismissed in advance.  

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