Ce qu’est la science
En science, il y a deux types de théories :
- Celles qui ont été prouvées fausses.
- Celles qui attendent d’être prouvées fausses.
Peu importe la quantité de preuves, une théorie ne sera jamais fiable à 100 %. En revanche, il suffit d’une seule contre-preuve pour l’invalider.
Par exemple, si tu affirmes qu’il n’existe que des cygnes blancs, peu importe la quantité de cygnes blancs que tu pointeras du doigt. Un seul cygne noir démolira ton argument.
Selon Popper, ce qui fait une bonne théorie scientifique n’est pas du tout sa capacité à trouver des éléments qui la confirment (on peut toujours trouver un cas qui confirme une fausse théorie), mais le fait qu’elle soit réfutable, sans parvenir pour autant à la réfuter, ce qui augmente sa crédibilité.
It is easy to obtain confirmations, or verifications, for nearly every theory–if we look for confirmations. — Popper
Every ‘good’ scientific theory is a prohibition: it forbids certain things to happen. The more a theory forbids, the better it is.
Ce qu’est la pseudo-science
A theory which is not refutable by any conceivable event is nonscientific. Irrefutability is not a virtue of a theory (as people often think) but a vice.
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.
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’.)
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. (I later described such a rescuing operation as a ‘conventionalist twist’ or a ‘conventionalist stratagem’.)
Finally, Popper was careful to say that it is impossible to prove that Freudianism was not true, at least in part. But we can say that we simply don’t know whether it’s true because it does not make specific testable predictions This is the essential “line of demarcation,“ as Popper called it, between science and pseudoscience.