Commensurability is a concept in the philosophy of science. Scientific theories are described as commensurable if one can compare them to find out which is more accurate. If there is no way one can compare them to determine which is more accurate, they are incommensurable.

Behind this is the idea that it is possible to see the world in multiple ways, and that there is not one fair method to see which way is right. Some think that scientific traditions (or paradigms) can be incommensurable: it is not really possible to say which one is right. This idea has been defended by Thomas Kuhn. He wrote: when paradigms change, the world changes with them. Paul Feyerabend was another philosopher who said that incommensurability was possible in scientific topics. He wrote that it is important to remember this, because it means that it is possible to say things that are not scientific, but also not wrong.^[1] These ideas were mainly aimed at Karl Popper and his ideas on falsification.

Two theories may not be comparable if one cannot find a way to compare them and decide which is right.

The concept of incommensurability is dramatized in the 2006 movie Idiocracy,^[2] when U.S. Army scientist Joe Bauers attempts to explain before a full Cabinet meeting his theory that the nation's crops would be better irrigated with water rather than with a sports drink.