Karl Popper – Philosopher of Science

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Karl Popper (1902 – 1994) was perhaps the most influential philosopher of science active during the 20th century remembered for his works on the scientific method and politics (1). Some of his writings attempted to separate actual science, based on certain criteria, from metaphysical or mythological claims (2).

Popper is well-known for his falsificationist methodology which states that for something to be considered a scientific theory it must make predictions that future observations could possibly reveal to be false (3). This means that purported hypotheses supported by untestable ad hoc hypotheses and which are immune to being falsified cannot be considered scientific. However, if an observation does in fact falsify a theory or parts of a theory then scientists are required to revise the theory or reject it in favour of a rival theory. As such, theories are open to criticism and the scientific community has the task of testing them to determine whether or not they can withstand critical scrutiny. For Popper, the more predictions a theory makes the better the theory is. Popper also maintains that it is never possible to “prove” a scientific theory; rather, it could only be falsified and no amount of positive experimental testing can prove a theory true although a single counterexample can show it to be false. In his Conjectures and Refutations, Popper contends that for a hypothesis to obtain the status of a theory it must be open to being falsified, refuted, and/or tested, which he presents in seven steps (4):

1. It is easy to obtain confirmations, or verifications, for nearly every theory – if we look for confirmations.

2. Confirmations should count only if they are the result of RISKY PREDICTIONS; that is to say, if, unenlightened by the theory in question, we should have expected an event which was incompatible with the theory – an event which would have refuted the theory.

3. Every ‘good’ scientific theory is a prohibition: it forbids certain things to happen. The more a theory forbids, the better it is.

4. A theory which is not refutable by any conceivable event is non-scientific. Irrefutability is not a virtue of a theory (as people often think) but a vice.

5. Every genuine TEST of a theory is an attempt to falsify it, or to refute it. Testability is falsifiability; but there are degrees of testability: some theories are more testable, more exposed to refutation, than others; they take, as it were, greater risks.

6. Confirming evidence should not count EXCEPT WHEN IT IS THE RESULT OF A GENUINE TEST OF THE THEORY; and this means that it can be presented as a serious but unsuccessful attempt to falsify the theory (I now speak in such cases of ‘corroborating evidence’.)

7. Some genuinely testable theories, when found to be false, are still upheld by their admirers – for example by introducing AD HOC some auxiliary assumption, or by re-interpreting the theory AD HOC in such a way that it escapes refutation. Such a procedure is always possible, but it rescues the theory from refutation only at the price of destroying, or at least lowering, its scientific status.

Popper also claims to solve the Scottish philosopher David Hume’s problem of induction. This was a philosophical problem that Hume popularized in the 18th century (5). Induction is the process of arriving at theories, laws, and generalizations based on observing regularities in experience. Hume objects to this stating that induction can’t be justified rationally. Popper agrees with Hume stating that he “approached the problem of induction through Hume. Hume, I felt, was perfectly right in pointing out that induction cannot be logically justified” (6). However, Popper argues that it is mistaken to assume that scientific generalizations are conclusions. He also maintains that Hume’s problem of induction misunderstood how scientists went about forming hypotheses (7). Popper argues that instead of generalizations being considered conclusions, they rather have the logical status of conjectures. Generalizations are not supported or justified by observations, thus resolving Hume’s problem of induction. In this way, generalizations are put to the test as they are first conjectured then held up to the scrutiny of experience for refutation.

Throughout his career, Popper penned several important works. The Logic of Scientific Discovery (1934) is arguably his most important philosophical writing in which he fleshes out his concept of falsificationalism as a scientific methodology. He further elaborates on other scientific concepts such as theories, corroboration, testing, probability, and quantum theory. The Open Society and its Enemies (1945) presents Popper’s own view of a functioning society in which he both defends liberal democracy and criticizes views presented by other notable figures. Criticism is leveled at the Ancient Greek philosopher Plato as well as the 19th century political theorist and philosopher Karl Marx. Conjectures and Refutations (1962) further extrapolates on his falsificationist methodology and applies it to both the philosophy of science and political philosophy. In his work The Poverty of Historicism (1957), Popper examines and criticizes historicist views he argues underpin most forms of authoritarianism and totalitarianism, and also provides an exposition on the scientific method and social science.


1. Shea, B. Karl Popper: Philosophy of Science. Available.

2. Shea, B. Ibid.

3. Stokes, P. 2007. Philosophy: The Great Thinkers. p, 209-210

4. Popper, K. 1962. Conjectures and Refutations. p. 34-37.

5. Stokes, P. 2007. Ibid. p. 209.

6. Popper, K. 1962. Ibid. p. 55

7. Stokes. Ibid. p. 209-210


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