This paper examines Karl Popper's proposed solution to the demarcation problem — the challenge of distinguishing science from non-science — through his criterion of falsifiability. It explains why Popper rejected Hume's inductive method in favor of the view that genuine scientific theories must be refutable by conceivable counterevidence. The paper then compares Popper's framework with Thomas Kuhn's account of scientific revolutions, highlighting both the shared emphasis on problem-solving and the key differences regarding how anomalies drive theory change. While Popper demands logical refutation as the standard, Kuhn argues that paradigm shifts are shaped by cultural and historical circumstances rather than pure logic.
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According to the philosopher Karl Popper, "the central problem in the philosophy of science is that of demarcation, i.e., of distinguishing between science and what he terms 'non-science'" (Thornton 2009). Colloquially, of course, most of us think we know what science is — it is the scientific method, or the proving of a hypothesis. But even here there is confusion, given that what constitutes a scientific "theory" is not what is meant by "theory" when a layperson speaks. Much of what we intuitively believe to be science may not be science at all, given that it may be based more upon observed correlations and personal experiences than the proving and disproving of hypotheses. According to Popper, what we call science is largely a web of hypotheses rather than "truth."
Popper called the problem of distinguishing between science and non-science a problem of demarcation. He was unusual among philosophers of his era in taking seriously Hume's critique of scientific induction: "Our knowledge of such contingent truths could only be grounded in our experience. But the principle of the uniformity of nature isn't something that we can just 'see' to be true. As a result, it appears that we could only have inductive evidence to support it. So it seems that the only way we could justify anything like the inductive principle is through induction" (Beisecker 2005). Although our presumptions may be accurate much of the time, they are hardly true all of the time.
Popper's critique builds on Hume's insight by arguing that pure, objective inductive observation is not, in fact, the foundation of all scientific theories. "All observation is selective and theory-laden — there are no pure or theory-free observations" (Thornton 2009). Observation takes place only with a purpose, whether that purpose is a consciously designed experiment or everyday experience. There is no unique scientific methodology that stands apart from conventional observation. All human activity "consists largely of problem-solving," whether the problem is theoretical or practical (Thornton 2009). Science is based on problems, not observations, and observations are scientifically meaningless unless they are designed to solve problems.
This problem-solving approach, however, can be riddled with errors, driven by the human desire to prove a particular theory true or false. It is very easy to find evidence in support of a hypothesis, regardless of how erroneous it might be, and it is virtually impossible to be exposed to all instances of a given phenomenon. Instead of the inductive method, Popper therefore proposes falsifiability as the standard for any scientific theory.
"For Popper, a theory is scientific only if it is refutable by a conceivable event. Every genuine test of a scientific theory, then, is logically an attempt to refute or to falsify it, and one genuine counter-instance falsifies the whole theory" (Thornton 2009). Popper's theory of falsification and his rejection of the inductive method also provides a superior way of dealing with scientific phenomena that cannot be observed in their entirety. "It is logically impossible to conclusively verify a universal proposition by reference to experience (as Hume saw clearly), but a single counter-instance conclusively falsifies the corresponding universal law. In a word, an exception, far from 'proving' a rule, conclusively refutes it" (Thornton 2009).
A theory is just that — a theory — which receives additional corroboration based on experience. More and more empirical evidence mounts in support of the theory until, finally, it is either falsified by a contradictory example or a better theory supplants the original one. "In practice a single conflicting or counter-instance is never sufficient methodologically to falsify a theory," but when the counter-instances outweigh the original support, the theory gradually begins to be questioned (Thornton 2009).
"How theories are built, tested, and replaced"
"Popper classifies psychology and astrology as non-science"
"Kuhn introduces paradigms, anomalies, and scientific crises"
"Key philosophical differences between Popper and Kuhn"
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