QuestionsCan science explain everything?Scientific revolutions: changing paradigm is not proving
Can science explain everything?A human construction

Scientific revolutions: changing paradigm is not proving

Paradigms and incommensurability (Kuhn)

Thomas Kuhn 1922 · 1996Science advances by revolutions: one paradigm replaces another.
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What it claims

The transition from one paradigm to another cannot be forced step by step by logic and experience alone: it requires persuasion, and one cannot strictly prove that the new framework is better.

Why

Rival paradigms share neither criteria nor vocabulary: so no neutral proof can settle between them.

In short

"Scientific revolutions: changing paradigm is not proving" is an argument by Thomas Kuhn (The Structure of Scientific Revolutions, 1962, 2nd ed. 1970) on the question "Can science explain everything?" (answer: a human construction). Its claim: The transition from one paradigm to another cannot be forced step by step by logic and experience alone: it requires persuasion, and one cannot strictly prove that the new framework is better. According to AskPhilosophy's logic check (Z3 solver), the conclusion does follow from its 3 premises. AskPhilosophy presents 3 objections, 3 of them with a documented reply, and the original text behind each premise, checked word for word.

The Structure of Scientific Revolutions, 1962, 2nd ed. 1970
Valid

Science is often pictured as a staircase: each generation adds steps of secure truths. The physicist and historian of science Thomas Kuhn showed in his 1962 book that history looks more like a series of breaks. For long periods, scientists work inside a shared framework he calls a "paradigm" (for example Newton's physics). Then anomalies pile up, and another paradigm replaces the first (Einstein). Kuhn adds that the two frameworks are "incommensurable": they do not pose the same problems, do not have the same standards of success, and do not always give the same meaning to the same words. So moving from one to the other is not done by a proof everybody must accept. For Kuhn, what escapes proof here is the choice of the framework itself. Careful: he never said that science is irrational or that anything goes. He repeated this in his 1969 postscript: this is the main objection he faced (Popper, Lakatos), and he answered it.

P1Scientists normally work inside a paradigm: achievements recognised by all, which for a time provide model problems and solutions to a community of practitioners.
P2Scientific revolutions are episodes in which a paradigm is replaced, in whole or in part, by an incompatible one: knowledge does not simply add up.
P3Two rival paradigms are incommensurable: they agree neither on the list of problems to solve, nor on the standards of a good solution, nor quite on the meaning of words, so that their supporters work, in a sense, in different worlds.
P4 · implicit premiseWhen two camps do not share the standards or vocabulary that would allow a decision, no neutral proof, accepted by both, can decide between them.
Therefore the transition from one paradigm to another cannot be forced step by step by logic and experience alone: it requires persuasion, and one cannot strictly prove that the new framework is better.

click a premise to reject it

If you accept every premise, logic forces you to accept the conclusion. So the debate is about the premises.
Checked by a logic solver: the premises cannot all be true while the conclusion is false.
Without the implicit premise: Without P4, one could admit that paradigms differ and still say that one theory wins by neutral proofs: both camps agree on a crucial experiment, such as measuring the bending of light near the Sun, and one of them must then yield.
The argument is valid: P1 and P2 describe the case (two paradigms replacing each other), P3 says that they are then incommensurable, and P4 that incommensurability rules out neutral proof. All the debate is about P3 and P4. Popper challenges P3: two rival theories can be compared, for instance those of Ptolemy and Copernicus. Lakatos and others fear that P4 makes the choice irrational. Kuhn answers that strict proof is an ideal of logic or mathematics, not the only form of reason: good reasons remain (accuracy, simplicity, fruitfulness) which, he says, weigh for the group of specialists.
Analogy. Two teams play on the same field, but one plays football and the other rugby. Neither can show it "played better" using the other's rules. To change games, the players must be given reasons to prefer other rules: that is a work of persuasion, not demonstration.

Objections

3

Each objection is a conversation: click to see who replies and where the debate stands.

Karl Popper ("The Myth of the Framework", text conceived in the mid-1970s) 1994 · attacks premise 3

A theory better than the previous one must be comparable with it: two theories are therefore not "incommensurable", to use Kuhn's term. For example, Ptolemy's astronomy is far from incommensurable with Copernicus's. There is indeed, psychologically, a change of outlook (Popper grants Kuhn's "Gestalt shift"), but the two systems can be compared logically: Copernicus argued that all observations that fit a geocentric system also fit a heliocentric one.

Kuhn replies
Thomas Kuhn 1970 · Kuhn's reply (Postscript of 1969)
Kuhn specifies that he never said researchers from rival camps cannot talk to each other. Their communication is only partial, because they use almost the same words while attaching them a little differently to things. The solution, he writes, is that each recognises the other as a member of a different language community, and then becomes a translator: this is what the historian of science does with old theories.
Karl Popper 1994 · Popper accepts the correction but keeps his diagnosis (end note of the same essay)
Popper writes in a note that while writing this part he first had Kuhn in mind, but that, as Kuhn points out, this interpretation was based on a misunderstanding. He says he is quite ready to accept this correction. He adds, however, that the view he discusses in this section remains, in his opinion, influential.
The debate goes on (our summary) The debate goes on. Popper thus withdraws the accusation made against Kuhn himself, but keeps his opinion on the influence of the view he criticised (see also the relativism objection below). Neither side has won.
I
Imre Lakatos (1970) 1970 · attacks premise 4

Lakatos sums up Kuhn's position like this: a new paradigm brings its own standards, there is no standard above paradigms, and the change from one to another is irrational, a matter of "mob psychology". If P4 is true, science would stop being a matter of reasons and become a matter of fashion or collective bandwagon.

Kuhn replies
Thomas Kuhn 1970 · Kuhn's reply (Postscript of 1969)
Kuhn replies that his point is simple and familiar: debates about theory choice do not look like a proof in logic or mathematics, where the rules are fixed at the start. This implies neither that there are no good reasons for being persuaded, nor that those reasons are not decisive for the group. These reasons are the usual criteria of the philosophy of science (accuracy, simplicity, fruitfulness), but they function as values, which can be applied in different ways.
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Imre Lakatos 1970 · Lakatos's counter-proposal (1970, in the same article)
Lakatos does not merely criticise Kuhn: he proposes an objective criterion for judging rival research programmes. A series of theories is "progressive" if each new theory predicts new, unexpected facts and if some of these facts are confirmed; otherwise it is "degenerating". This would give reasons for choosing that are not mere values.
The debate goes on (our summary) The debate goes on (our summary). Kuhn's defenders object that judging "progressive" or "degenerating" itself requires choices (how long to wait for a success?) that the criterion does not settle. Neither side has won.
Kuhn's critics (including Shapere and Popper, cited by Kuhn) 1970 · attacks the conclusion

Many readers found Kuhn's viewpoint relativistic. If communities of researchers each live in their own world and cannot be told apart by proofs, it seems that each community is right in its own way, and that science does not get closer to any truth.

Kuhn replies
Thomas Kuhn 1970 · Kuhn's reply (Postscript of 1969)
Kuhn separates two things. For cultures, he nearly accepts the word "relativistic": groups are like different language communities, each of which may be right in its own way. For science, he refuses the word: later theories are better than earlier ones at solving puzzles, and the development of science goes in one direction, never doubling back. He calls himself a convinced believer in scientific progress.
Thomas Kuhn 1970 · What Kuhn does not claim (same postscript)
Kuhn himself adds a limit: it is often said that a theory is better because it represents better what nature is really like. He sees in the succession of theories no coherent direction of development toward what really exists. The progress he speaks of is thus that of a tool for solving problems, not a demonstrated approach to truth.
The debate goes on (our summary) The debate goes on (our summary). Realists hold that this limit gives the critics their point back: if science does not get closer to the truth, can we speak of progress other than practical? Kuhn holds he needs only that kind of progress. Neither side has won.
What today's voices say
Criticize it
Steven PinkerAgainst the idea that science is always overturned: "Einstein may have overturned Newton in a sense but Newton's laws of gravity still describe the motion of a baseball". Scientific revolutions keep what worked.
Karl PopperKuhn's Structure of Scientific Revolutions denied that science grows by testing and refuting; Popper's approach was overshadowed by it.