Karl Popper


The Austrian philosopher, Sir Karl Raimund Popper, radically changed the way science is perceived by the philosophical community and it is impossible to ignore his views regarding what is known as the philosophy of science. The primary problem with which Popper is concerned is the demarcation between the science and the non-science. What are the characteristics of a theory or an idea which leads us to classify it as scientific or non-scientific? Why is it that Spinoza’s view of the universe is considered as metaphysics, while Einstein’s theory of Relativity is considered as a scientific theory?

Many earlier thinkers had considered induction to be the distinguishing characteristic of a scientific theory. These people believed that scientists made observations and then formed a scientific theory to explain these observations. Then there were certain philosophers among the logical positivists, who believed that a scientific theory had the property of verification. That is, the theory made a certain predication, and if that prediction matched with the observation, it meant that the theory was verified as true.

Karl Popper, however, rejected this classical observationalist-inductivist account of science. Popper did not believe that scientists really used induction to make scientific theories, or if they used it, its role was not central. Scientists do not begin, Popper thinks, with observations but rather with problems. All observations are selective and theory-laden - there are no pure or theory-free observations. And since a certain theory precedes observation, how can it be said that it is observation which is the first step in the formation of a new scientific theory? In this way Popper repudiates inductive method as the proper mechanism by which scientific theories are formed, and therefore induction is not the distinguishing character of a scientific idea.

Popper denied the idea that any scientific theory can ever be verified as true. To the contrary, Popper believed that the only sure test of a theory being as scientific was its quality of being potentially falsified. A theory is to be considered scientific only and only if it is capable of being falsified.

Why a scientific theory cannot be verified is because of its universality. Referring to the example we discussed in Hume, let us consider a statement like ‘All crows are black’. Now this is a statement which can never be verified by no matter how many observations we make, because the hypothesis of crows being black extends to all existing crows, which may be beyond the reach of our observation. And therefore, this statement can never be conclusively verified. Discovering a black crow every time we make an observation does not confirm the theory, but only makes it more probable; the confirmation is only provisional. On the other hand, this statement can be conclusively rejected or falsified. It would take a single observation of a white crow [or red, or any other colour] to finally prove that this theory is wrong. This asymmetry between verification and falsification is central to Popper’s account of science i.e. a theory can be falsified but not verified.

A genuine scientific theory is therefore one which is prohibitive, i.e. it prohibits certain observations or events, which if happen would falsify the theory. Any theory which doesn’t contain any criteria of its falsification, and therefore explains everything, cannot be called as scientific. This can be explained by a rather crude example. Let us think of a doctor who is testing a new medicine as a treatment of a certain disease. The doctor begins to treat the patients of this disease by giving them this new medicine. Now, whenever a patient survives the disease and is cured, the doctor thinks of it as proof that the medicine has the healing properties. On the other hand, if the patient under treatment dies, the doctor assumes that the stage of the disease was too severe for the patient to be cured. Just think for a moment under the light of what has been written in this chapter what is wrong with this methodology. The answer is that the doctor has left no room at all for the falsification of his theory that the medicine had a curative effect. He has thought up of no potential observation which would prove that the medicine is not working. By forming this all-encompassing theory, his approach is no longer scientific. It is quite possible the patients who survived the disease did because of their own natural immunity rather than by any aid of the medicine. It is also possible that the medicine might even have a negative effect on the patient, and that the medicine might have even contributed to the deaths of the unfortunate patients. As obvious, if this principle of falsification is ignored, it can lead to all sorts of pseudo-sciences.

The famous astrophysicist Stephen Hawkings explains this view in this manner:
“…a scientific theory is a mathematical model that describes and codifies the observations we make. A good theory will describe a large range of phenomena on the basis of a few simple postulates and will make definite predictions that can be tested. If the predictions agree with the observations, the theory survives that test, though it can never be proved to be correct. On the other hand, if the observations disagree with the predictions, one has to discard or modify the theory.”[1]

“Any physical theory is always provisional, in the sense that it is only a hypothesis: you can never prove it. No matter how many times the results of the experiments agree with some theory, you can never be sure that the next time the result will not contradict the theory. On the other hand, you can disprove a theory by finding even a single observation that disagrees with the predictions of the theory.”[2]

Another important aspect of Popper’s scientific view is that Popper considers the formation of a scientific hypothesis a creative and imaginative process. There is just no ‘scientific method’ by which a scientist can form a hypothesis. He has to be original and creative, and to use his imagination. It shows the role creativity and imagination has to play in the progress of science. Great scientific theories like theory of Relativity and Quantum Mechanics are the result of the spontaneous and intuitive ideas of the scientists. It is this creative aspect of Popper’s scientific method which has been admired by the scientists, and has also been a factor leading to the popularity of this point of view.

In Popper’s terminology, a ‘basic statement’ is to be treated as a particular observation report. A genuine scientific theory, therefore, divides a class of basic statements into two non-empty sub-classes.
1) The class of basic statements which the theory prohibits, and whose occurrence would disprove the theory. Therefore these are the potential falsifiers.
2) The class of basic statements with which the theory is consistent, and which do not verify the theory.
[This is just the expression of the logical asymmetry between verification and falsification, as explained above.]

Popper now faces the task of explaining the growth of science as observed in history on the basis of his scientific method. Popper believes that science advances in an evolutionary manner, on the principle of selection and the survival of the fittest. It is a game of conjectures and refutations. Popper describes this with a formula:

PS1 -> TT -> EE -> PS2

In a response to any problem situation [PS1] the scientists present a number of tentative theories [TT]. These theories are now subject to critical examination and vigorous attempts of falsification. This is called error elimination [EE], and is a selective process which selects those theories which survive the critical tests posed by the investigators. The theories which are falsified are therefore rejected, and only the fittest of theories are allowed to go on. The theories which survive falsification are not true but only more fit. This leads to a gradual evolution towards more and more interesting problems [PS2] and the process of selection and falsification is carried on at each step. It is in this evolutionary manner that science advances, Popper believes.

Popper is perhaps unusual among contemporary philosophers in the sense that he accepts the validity of Hume’s denial of Induction. However, he does not share the resulting skepticism. Hume said that just because we have observed that A follows B does not mean that A will always follow B. Popper accepts that it is not necessary that A follow B, but we can theorize that A will follow B. If A follows B in all our observations, then although this theory is not verified, it has also not been falsified.
So, although it cannot be shown that sun will necessary rise tomorrow, we can make a theory that it will. If the sun doesn’t rise, the theory will be conclusively falsified. And if it does, the theory will be provisionally verified.
Similarly, although it can’t be shown that all crows are black, we can theorize that they are. If we observe a white crow, the theory will be falsified, otherwise it will survive.

There are a number of criticisms on Popper’s ideas. The immediate, perhaps the most effective is the realization of the picture of science it leads. The common sense view that the growth of science is a gradual accumulation of truth about the world is overthrown by this philosophy. Science is not an accumulation of truths, but rather an accumulation of unfalsified theories about the world, which may or may not conform to the Reality. Worse, this means that we can never prove that we have found a theory which really does explains things as they are. Even if our theory was correct, there is no way we could ever find out! What can be more destructive to science than this very realization that science does not offer us the truth regarding the world in which we live? John Searle writes:
“Most scientists do not, I think, realize how anti-scientific Popper’s views actually are. On Popper’s conception of science and the activity of scientists, science is not an accumulation of truths about nature, and the scientist does not arrive at truth about nature, rather all that we have in sciences are a series of so far unrefuted hypotheses.”[3]

One of the criticisms put forth is that Popper has clearly mentioned that there are no pure observations; observations are always ‘theory-laden’. The question arises that if the observations themselves are associated with theories, how can they be used to conclusively falsify another theory? For the Popper’s mechanism to work, it must be possible to conclusively verify the basic propositions as true or false, which would in turn lead to the falsification of the theory which prohibits them. But if it can’t be determined in the first place whether these basic propositions are actually true or false, the falsification becomes impossible to determine. In other words, unless it is shown that potential falsifiers are actual falsifiers, the falsification cannot be conclusive.

Here we must also understand that no theory is present in isolation but rather in association with many other theories. In case when an observation does not match with the prediction, any of the theories in the whole package can be wrong. So, which element of the package should the scientists consider to be falsified? Popper’s answer was that those theories which are more generally applicable are to be preferred, as they are more fit. As an example, he cited the discovery of Neptune. Slight disturbances in the orbit of Uranus were discovered which did not match with the predictions of Newtonian mechanics. But this did not falsify the Newton’s theory, because there was another theory associated with this case, which was of lesser value i.e. the idea that solar system has seven planets. Since the latter was of lesser general applicability as compared to Newton’s theory of Gravitation, it was this which was thought to be at fault. Adams and Leverrier showed that the disturbances in the orbit of Uranus could be explained by the presence of an eighth planet. They even calculated the precise location of the hypothetical planet, which was discovered exactly where they have proposed. This was hailed as a great triumph of Newton’s theory.

However, there is the objection raised by Popper’s own student Imre Lakatos that Popper assumes that there are such things as critical tests, which can conclusively falsify a theory. Popper had elaborated his idea of the critical test with his favourite example of the discovery of Neptune. In Popper’s view, the disturbances in the orbit of Uranus and subsequent explanation in terms of the eighth planet had posed a ‘critical test’ for the Newton’s theory which has passed with flying colours. Lakatos, however, denied that this was a critical test of falsification in the Popperian sense. He poses the question: what if the eighth planet had not been discovered? Would that have counted as a falsification of the Newton’s theory? Obviously, this would not been considered as a conclusive falsification of the Newtonian mechanics. There could have been a large number of other factors at work. There might have been an error in calculation, or the experiment might have been carried out properly, or it is also possible that there were a number of possible solutions to the disturbances of orbit of Uranus, apart from the presence of an eighth planet. The point is that theories like that of Newton can never be falsified as a result of isolated, individual non-confirmations. An experimental non-confirmation of a theory does not necessarily mean its falsification. In fact, such theories are highly resistent to falsification. Lakatos showed that generally applicable theories are falsified, not by critical tests as Popper had thought, but by the continuous incapability of the theory to explain the results of research programs and the theories are rejected only when the gap between the theory and the results of the research programs becomes unacceptable.

So it can be said that Popper’s view of falsification by means of critical tests is too neat to be applicable in actual scientific practice, although it contains many aspects which are quite valid, and whose significance and value is undeniable.

In ethics, Popper believed in a view called ‘negative utilitarianism’, which he developed in his work The Open Society and it’s Enemies. Utilitarianism seeks to increase the maximize good by increasing the happiness of the people, setting its goal as ‘greatest happiness of the greatest number of people’. But Popper stresses the importance of minimizing evil in contrast to maximizing good, and he believes that attempts to decrease evil would produce far better results in society than simply trying to increase the happiness of people.


[1] The Universe in a Nutshell by Stephen W. Hawkings, Page 31
[2] A Brief History of Time by Stephen W. Hawkings, Page 11
[3] The Future of Philosophy, an article by John Searle.