The Logic of Scientific Discovery
(1934)
Karl Popper


When Logik der Forschung was published in Vienna in 1934, Karl Popper was only 32, and working as a secondary school teacher – slightly surprising given the book’s huge influence on 20th century thought. The Logic of Scientific Discovery (as the title was translated in 1959) put the philosophy of science on a firm footing, and figures such as Imre Lakatos, Paul Feyeraband and Thomas Kuhn followed in its wake.

The Vienna of Popper’s twenties was a place of intellectual and political ferment. Marxism and socialism were a popular cause among revolution-minded university students, including Popper, and the ‘Vienna Circle’ of logical positivists were trying to knock down the walls of philosophy with their demarcation between provable statements and metaphysical speculation. This intellectual richness would end with the rise of Nazism, and in 1937 Popper, who was brought up a Lutheran but had Jewish grandparents, fled to New Zealand where he took up a post teaching philosophy. There he wrote The Open Society and Its Enemies, his famous attack on totalitarianism, before moving to Britain where he reigned at the London School of Economics for 25 years.

The Logic of Scientific Discovery was a reaction against the language-analysing philosophy spawned by the Vienna Circle and typified by Wittgenstein, who had famously not even read Aristotle, believing that all philosophical problems could be solved through looking at language alone. Popper believed that the purpose of philosophy was to bring clarity to real world problems; it must seek to tell us something about our place in the universe. However, unlike engineering or some branch of physical science, in which you know what the problem is and you go to work on solving it, Popper said that philosophy has no ‘problem-situation’ – there is no groundwork of accepted facts onto which a new question can be placed. Therefore, he said, “whenever we propose a solution to a problem, we ought to try as hard as we can to overthrow our solution, rather than defend it.”

In other words, philosophy (and science) could no longer be about finding evidence to prove a theory – this wasn’t rigorous enough. A real philosopher or scientist would work to prove themselves wrong, attempting to find the holes in any existing theory. Only then might knowledge be worthy of its name.

The problem of induction, and its alternative: falsification

Popper saw a giant hole in philosophy and science: inductive thinking.

Inductive statements take a particular, and from it assert something universal. For example, from the observation that all the swans we have seen are white, we assert that ‘swans are white’. But we only need one case where this is not true (as for instance, when black swans were discovered in Australia) to realise that inductive reasoning is faulty.

But would it suffice for our knowledge to rest on ‘probabilities’? For Popper probability is a pseudo-scientific idea that doesn’t help the scientific project at all, because as an instance of inductive reasoning, probabilities are based on what has already happened, and tell us nothing certain about the future.

He makes the distinction between the ‘psychology’ of knowledge, which is about collecting, pointing out or making connections between facts – and the ‘logic’ of knowledge, which is about the testing of knowledge itself. If something is said to be true, how do you test it? Can it be tested?

For a theory to be considered genuinely scientific, it must be able to be proven wrong – falsified by anyone and with results that are reproducible. It is totally wrong to believe that your theory is ‘proven’, ‘verified’ or ‘confirmed’ if you can merely collect enough cases that seem to show it is true:

“Instead of discussing the ‘probability’ of a hypothesis we should try to assess what tests, what trials, it has withstood; that is, we should try to assess how far it has been able to prove its fitness to survive by standing up to tests. In brief, we should try to assess how far it has been ‘corroborated’.”

A theory is not a real one is if there is no way of testing it to see if it is false. Further, because he does not believe in induction, Popper says that theories are never ultimately and conclusively verifiable, they are only “provisional conjectures” which can find apparent corroboration.

Even positivism, which considered itself an ultra-empirical movement, fell for the inductive illusion, by claiming that something was only true if it could be show in a positive sense to be so. But this is not enough. Given the problems of inductive logic, to arrive at any semblance of knowledge you have to come at a problem from the negative angle, to relentlessly identify what clearly isn’t true. Popper admits that it may seem wrong-headed to go about science in a negative, falsifying way, but notes that scientific laws tend to have credibility when it is clear where they do not apply, or as he puts it, “the more they prohibit the more they say”.

Popper on metaphysics

From these arguments you begin to see how Popper raised the bar on science, separating nice ideas from bona fide theories. Yet he did so only because he believed in the scientific project. He described theories as “nets cast to catch what we call ‘the world’: to rationalize, to explain, and to master it. We endeavour to make the mesh ever finer and finer.” The fact that it is hard, even impossible, to ever arrive at total certainty should not stop us from trying to work out how the world works.

His demand for rigour did not, however, lead him to denounce metaphysics. The positivists’ claimed that they had killed off metaphysics because they had shown it to be meaningless, since no theological or spiritual idea can be tested by the senses or be made into an unimpeachably logical statement. But as Popper points out, many laws of natural science cannot be reduced to elementary statements based on sense information alone, and would not have been allowed to be put forward if the senses were our only criterion. “Indeed”, he writes, “I am inclined to think that scientific discovery is impossible without faith in ideas which are of a purely speculative kind, and sometimes even quite hazy; a faith which is completely unwarranted from the point of view of science, and which, to that extent, is ‘metaphysical’”.

Finally, he does not deny that a person can have a strong conviction about something, and that they may apprehend some truth, only that such a conviction, because its validity cannot be tested by anyone who wishes to, is not science. The ‘creative intuition’ that Bergson talked of, or ‘intellectual love’ as Einstein phrased it, are real enough in Popper’s view, but by their nature are not able to be logically analysed. Popper’s intention was not to overthrow metaphysics, only to properly demark genuinely empirical, testable questions from those that are not. Indeed, he noted, some things are not of a nature that they can be verified or falsified.

Final comments

Late in the book, Popper compares the scientific project to the erection of a city on water:

“Science does not rest upon solid bedrock. The bold structure of its theories rises, as it were, above a swamp. It is like a building erected on piles. The piles are driven down from above into the swamp, but not down to any natural or ‘given’ base; and if we stop driving the piles deeper, it is not because we have reached firm ground. We simply stop when we are satisfied that the piles are firm enough to carry the structure, at least for the time being.”

Though it may only be a structure “built on piles”, and even if it never gives us the certainty we crave, science is still valuable; that Venice is not built on bedrock does not lessen the fact that it is nevertheless a worthwhile place to be. The same goes for philosophy.

Popper’s conclusion is that “We do not know, we can only guess”, and those guesses are guided by the imagination and by a very unscientific faith that there are laws that underlie the universe. Fortunately, we have matured to a point where we know what systematic testing of ideas consists of, and need not be fooled by inductive thinking. If you fancy your hypothesis, give it the respect of doggedly trying to prove it wrong.    


Source: Philosophy Classics: Thinking, Being, Acting, Seeing, Profound Insights and Powerful Thinking from Fifty Key Books by Tom Butler-Bowdon (London & Boston: Nicholas Brealey).

Sir Karl Popper

Popper was born in Vienna in 1902. His father was a lawyer but also took a keen interest in the classics, philosophy, and social and political issues. His mother inculcated in him a passion for music, and he almost followed it as a career. 

At the University of Vienna he became heavily involved in left-wing politics and Marxism, but after a student riot abandoned it entirely. At this time he also discovered the psychoanalytic theories of Freud and Adler, and heard Einstein lecture on relativity theory (Einstein’s critical spirit, and its total absence in Marx, Freud and Adler’s work, impressed Popper). He got a primary school teaching diploma in 1925, took a PhD in philosophy in 1928, and qualified to teach mathematics and physics in secondary school the following year. Logik der Forschung attracted more attention than Popper had anticipated, and he was invited to lecture in England in 1935. 

He spent the next few years working productively on science and philosophy, but the growth of Nazism compelled him to leave Austria. In 1937 he took up a position at the University of Canterbury in New Zealand, where he remained for the duration of the Second World War. The annexation of Austria in 1938 became the catalyst for writing The Open Society and Its Enemies. In 1946 he moved to England, where he became professor of logic and scientific method at the London School of Economics. He was knighted in 1965, and retired in 1969, though he remained active as a writer, broadcaster and lecturer until his death in 1994.