A term coined by the philosopher of science Karl Popper in his work The Logic of Scientific Discovery (1934), signifying a standard basis of evaluation for scientific theories and hypothesis. A hypothesis is said to be falsifiable (or refutable) if it can be proven true or false by independent research using pre-existing empirical tests. If a proposition is falsifiable, then it can be accepted into scientific study, and other propositions or conclusions can build off of it. If it is not, it likely falls into the realm of non-science or pseudoscience.

Sagan introduces the concept in Chapter 10 with his thought experiment of the dragon in the garage. Since the friend’s claims of an “invisible, incorporeal, floating dragon” (171) cannot be falsified, Sagan cannot accept the existence of the animal. Without concrete evidence, it would be irresponsible to draw further conclusions about the wider existence of dragons. The concept of falsifiability is extremely important to Sagan’s wider argument, as it provides an early example of the type of proactive thinking that he encourages, and is part of his Baloney Detection Kit. Determining which claims are falsifiable is the first step of the skeptical apparatus, allowing scientists and careful thinkers to easily separate dubious claims from those requiring further research.