Philosophy of science

Philosophy · Logic, ethics and special topics. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.

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The idea

Philosophy of science asks what makes knowledge scientific and how science grows. Science generalises from observed cases, but Hume showed that no logical argument proves that the future will resemble the past. This is the problem of induction.

Popper replied that science does not need induction. A theory is a bold conjecture, and it is scientific only if it is falsifiable: it must forbid some possible observation. Scientists should try to refute their theories; one that survives severe tests is corroborated, never proved.

Kuhn looked at the history of science. Most work is normal science done inside a paradigm. Anomalies build up, a crisis follows, and a revolution replaces the old paradigm with a new one.

Rules to remember

Popper, 'The Logic of Scientific Discovery' (German 1934, English 1959): falsifiability is the line of demarcation between science and non-science.
Asymmetry: no number of favourable cases can prove a universal statement, but one true contrary case can refute it.
A theory that fits every possible observation forbids nothing and is not scientific in Popper's sense.
Kuhn, 'The Structure of Scientific Revolutions' (1962): normal science → anomalies → crisis → revolution (paradigm shift) → new normal science. Example: the change from the Ptolemaic to the Copernican system.
Hume: induction assumes the uniformity of nature, and that assumption can itself be supported only by induction.
Law = a statement of a general regularity; theory = an explanation of why the regularity holds.
Deductive-nomological model (Hempel and Oppenheim, 1948): an event is explained when it is deduced from laws of nature together with initial conditions.

Common mistake

Students write that a falsifiable theory is a false one. Falsifiable means only that some possible observation could show the theory to be wrong; a good theory is falsifiable and has so far not been falsified.

Worked example

A student answers Hume: 'Induction is reliable because it has worked very well in the past.' Why does this reply fail?

The reply moves from 'induction has worked in past cases' to 'induction will work in future cases'.
That step is itself an inference from observed cases to unobserved ones, which is an inductive inference.
So the reply uses induction to justify induction; it assumes the very thing it is meant to prove.

Answer: The reply is circular (it begs the question), which is exactly Hume's point: induction cannot be justified by experience without assuming it.

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