Karl Popper was an influential philosopher of science of the 20th century. He addressed issues related to how theories gain acceptance in science as opposed to how this happens in other fields of study. He argued that theories in science can not only be verified, but also make predictions which if shown to be false, would render the theory falsified. This principle which Popper called ‘falsifiability’, was to him, a hallmark of scientific hypotheses and theories.
Popper offered this criteria of falsifiability as a means of distinguishing science from non-science. The more the theory or hypothesis offers scope for it being disproved, and the more it has been subjected to attempts to disprove but has yet not been disproved, the more it is scientific, as per Popper. On the other hand, if they do get disproved, and scientists attempt to trace the source of the error, make modifications, and present another version of the theory (or an entirely new theory) which also makes predictions that can be disproved by future observation, Popper would consider it a candidate for a scientific theory. By constantly being put to the test in this manner, science acquires continuous refinement according to Popper.
To better appreciate Popper’s work, it is fruitful to examine the state of philosophy of science before him. Many philosophers before him had stressed on the role of ‘inductive inference’ as a means of arriving at scientific conclusions. An example of an inductive argument is as follows-
Premise 1) I press a certain switch and a certain bulb glows.
Premise 2) I press the same switch again and the same bulb stops glowing.
Premise 3) I press the switch on and off many times, and each time, the bulb goes on and off with it.
Inductive Inference: Everytime this switch is pressed the status of the bulb switches between on and off.
Note how in this way of inferring, based on a limited number of observations, a generalisation is drawn for all possible observations. This was considered to be the process by which scientific conclusions were drawn. But in the 18th Century, David Hume pointed out that inductive inference relies heavily on the assumption that the future will be like the past, which he said, cannot be justified. No reason can be offered for why the switch will continue to do what it did before to the bulb. It is possible that one day, the bulb stops responding to the switch. Similarly all the scientific knowledge accrued through the use of inductive inferences may just one day cease to be true. Hume’s point was that unlike deductive reasoning, the conclusions drawn from inductive reasoning do not follow necessarily from the premises. After Hume, philosophers of science tried various ways to justify inductive inference, and thereby, what they thought to be the scientific method.
Popper, on the other hand, did not try to refute Hume’s argument. He agreed that no matter how many observations were made, it would not be possible to conclude on observations not yet made. He appends this argument with his criterion of falsifiability to demarcate scientific theories from non-scientific ones. He points out the futility in attempts to prove theories by induction and instead encourages attempts to falsify them. To Popper, non-scientific theories were theories totally immune to being shown to be false by any future observation. He clubbed theories such as psychoanalysis, astrology, and marxism as ‘pseudo-sciences’ as they are compatible with every possible observation, and cannot be disproved.