Semmelweis Reflex
We reflexively reject new evidence that contradicts established norms or deeply held beliefs.
The Semmelweis reflex is the metaphorical term for the tendency to reject new evidence that contradicts established norms, beliefs, or paradigms. It is named after Ignaz Semmelweis, a 19th-century Hungarian physician who discovered that hand-washing prevented puerperal fever. His colleagues, unwilling to accept that they were responsible for patient deaths, rejected and ridiculed his evidence. His theory was only validated after his death.
What it looks like in the wild.
- Everyday life Dietary Science Resistance Established nutrition experts often reject new dietary science (e.g., about saturated fats) because it contradicts decades of their published work.
Recognising a definition is not the same skill as spotting it.
Two scenarios from the app, with distractors drawn from the same family of biases — which is what makes them hard.
A person rejects evidence that their pet's breed has inherent health problems, because acknowledging the genetic predispositions would mean their choice of breed may have been irresponsible and could result in suffering for an animal they love.
A politician rejects a climate change report because it contradicts the economic policies they've championed for decades.
Biases rarely arrive alone.
Understand more. Assume less.
188 biases, 18,869 scenarios, and a record of how you actually decide.
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