The Real Meaning of Falsifiability

Karl Popper’s “criterion of demarcation” classifies a theory as scientific only if that theory could conceivably be contradicted (“falsified”) by a logically possible observation. Intellectuals nowadays commonly deride theories as “unfalsifiable”, brandishing the term as a pejorative. But falsifiability was never intended as a criterion of value or meaning. It was merely a technical distinction between different types of theories that address different kinds of questions and that, as a result, are vulnerable to different modes of criticism. In particular, it distinguishes one class of theories from all others: universal laws of physics. A theory in this class has a special attribute: it can be logically contradicted by the observation of a single event that it says could never occur. Most good theories—including the theory of falsifiability itself—do not fit into this class. But we can still assess unfalsifiable theories rationally, using modes of criticism besides observation and experiment. And many such modes are available. For example, we can assess such theories using criteria of explanatory power, logical coherence, and consistency with other theories. But to assess conjectured universal laws of physics, we can also attempt to devise a situation (i.e., an experiment) in which we observe a physical event that the theory forbids. If we observe that event, then we will have discovered that the world does not conform to the theory. So, scientific theories are “demarcated” from other kinds of theories in one respect, which falsifiability is just a way of expressing: namely, they are subject to every mode of criticism that other theories are subject to plus observation and experiment. And this added mode of criticism can accelerate the growth of knowledge in science as compared to other fields because more criticism promotes more error correction, which is what fuels the growth of all knowledge, scientific or not.

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