How does “You can’t prove a negative” work?
In: Mathematics
“You can’t prove a negative” is an adage typically said when accusing a person of trying to shift the burden of proof, particularly involving an unfalsifiable claim. As a famous example, if I were to claim there was a small teapot in space (too small to be detected by our current instruments) and asked you to prove me wrong, you might reply that you can’t prove a negative as there is no practical way for you to scour all that space to prove there are no teapots there, while I could easily prove there is by showing some evidence, such as a photograph or the teapot itself.
As with most adages, it is not always accurate. For example, there is a medical blood test called a d-Dimer that is sometimes useful for testing whether a patient has a blood clot, which sometimes can be deadly. The d-Dimer can prove you don’t have a clot with a negative result, but it does not prove anything with a positive result, so it is an example of a situation in which you can prove a negative but not a positive.
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