Written by and shared with permission of Alan Forrester

Karl Popper made many great contributions to epistemology and political philosophy, largely as a result of poppertaking fallibilism seriously. Popper argued against justificationism - the idea that we can and should show that our knowledge is true or probably true. Popper’s first contribution was his solution of the problem of induction. Following the scientific revolution in the late seventeenth century, we gained a lot of scientific knowledge and philosophers wanted to explain that knowledge. Their answer was inductivism: using a process called induction scientists observe the world, use those observations to come up with theories, and then show that those theories are true or probably true. The problem of induction is that there cannot be any such process. Popper pointed out that before you can make observations you have to have ideas about what to observe, and so the theory must come first rather than being worked out from observations. It follows that all observations are theory laden and we can’t prove anything using them because our interpretation of them may be wrong. Also, theories don’t follow from observations since theories have many consequences for events that nobody ever observes, like what is happening in the core of the sun. Popper solved this problem by proposing that knowledge is created by conjectures and refutations. We make guesses about the processes occurring in the real world and criticise those guesses in terms of whether they provide good explanations. As part of our criticism we work out the consequences of those guesses and then try to do experiments to test whether those consequences actually happen. We use experiments to criticise theories, not to justify them.

Popper extended his epistemology to philosophy as well, arguing that good philosophy starts with problems that arise outside philosophy. The problem of induction arose from the success of science, but it is not a scientific problem because it can’t be settled by observations or experiments. Indeed the significance and interpretation of the evidence is one of the points at issue. Popper also argued more broadly that his criticism of inductivism also fatally wounded all other theories that purport to show that there are authoritative sources of knowledge - that is, all justificationist theories of knowledge. The utility of all such sources depends on people interpreting them correctly, and so it is impossible to show that any theory is true or probably true. Instead we must make progress by proposing solutions to problems and then criticising those solutions.

Popper provided many guidelines to help people create knowledge more easily. For example, any proposal to explain an experimental result that seems to clash with a theory should be independently testable: it should make predictions about some problem other than the one it was meant to solve. For example, Einstein's theory of gravity, general relativity, made a correct prediction about the orbit of Mercury that Newton's theory of gravity didn't make. Einstein's theory of gravity also made many other predictions that were different from Newton's theory, such as predictions of how the wavelength of light changes when it falls through a gravitational field. So it's easier to do experimental tests of Einstein's theory than it would be to experimentally test a theory that said "Newton's theory is right except for the orbit of Mercury" and made no other predictions.

Popper also argued that useful knowledge is objective rather than subjective. A lot of knowledge is contained in books: this is useful because people can argue about the content of knowledge that is written down more easily than they can argue about the content of a thought. Also, other biological organisms instantiate knowledge about how to propagate genes in particular environments, but they do not understand that knowledge. Biological knowledge is created by variation (mutation of genes) and selection (whether the resulting phenotype can make copies of those genes).

Popper applied his epistemology to political philosophy too. He pointed out that no single person or group is always right, so we should not be interested in the traditional question of political philosophy: ‘Who should rule?’ He noted that this formulation of the fundamental question in politics is rather like the question that is often regarded as fundamental in epistemology (What is the infallible source of our knowledge?). In each case the question is not well put. In the same way that all our sources of knowledge are fallible, so all forms of power are likely to be used to implement bad ideas. Rather, we should expect any ruler to make mistakes and ask how we can arrange our institutions to prevent bad or incompetent leaders and bad policies from doing too much damage. He considered democracy valuable insofar as it allows us to remove leaders from power and replace their policies without violence. Violence is bad because it prevents people from solving problems. If you use violence to get people to do what you want then they can’t act on any objections they have to your proposal, and so the corresponding problems will not be solved. This removes a means of improving your policies. And even if the policy is a good idea people will be inclined to act in a way that undermines it either because they want to undermine the policy deliberately, or because they don’t understand the policy. This could be called a "minimal" theory of democracy. It is not based on the assumption that any serious problem is solved by democracy alone, it is merely a framework where the leadership can be changed without resort to violence. People have to solve problems - "democracy" does not solve them.

Popper also attacked historicism: the idea that it is possible to predict the future using laws of history analogous to the laws of physics. He pointed out that the future depends on our actions and so depends on our knowledge. We can’t know what knowledge because if we did we would already have it, so we can’t predict the future course of history either. This implies, in particular, that we can’t predict the results of a proposed reform. We should try to make piecemeal changes so that we can more easily change policies in the light of problems instead of trying to sweep away current institutions and build new ones from scratch.

Popper was an optimist too. He argued that the world is better now than at any other time we know of and that we may be able to make the future even better by improving our ideas.

Further reading

Karl Popper, Realism and the Aim of Science, Routledge, London.

Karl Popper, Objective Knowledge: An Evolutionary Approach, Revised Edition, Oxford University Press. New York.

Karl Popper, The Open Society and Its Enemies Volumes 1 and 2, Routledge, London.

Karl Popper, Conjectures and Refutations, Routledge, London