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Brief Lives

Thomas Kuhn (1922-1996)

Will Bouwman considers the development of a paradigmatic revolutionary.

In 1962 Thomas Kuhn published a book from which the philosophy of science has not yet recovered, and probably never will. Before this book it was generally assumed that the only history that was relevant to science was recent. Science was believed to be a relentless march towards the truth, every innovation an advance. Scientists may have been standing on the shoulders of giants (to quote Isaac Newton), but every change was assumed to be taking us higher. Ironically, Kuhn the philosopher did what a good scientist does, and actually looked at the evidence. What he saw was that far from being the steady, uniform accumulation of objective truth about the way the world functions, the history of science is punctuated by moments when the prevailing consensus is completely shattered. His first book, The Copernican Revolution (1957), detailed the events and causes of one of the most graphic examples of this. Kuhn expanded on this picture to provide his general model of the nature of scientific progress in The Structure of Scientific Revolutions.

Thomas Kuhn portrait by Davi.Trip 2018

Normal, and Revolutionary, Life

Thomas Samuel Kuhn was born on July 18 1922 in Cincinnati, Ohio. His father, Samuel, a veteran of World War I, was an industrial engineer and investment consultant whose wife, Minette (née Strook), was a graduate of Vassar College who wrote for and edited progressive publications. Both parents were active in left-wing politics, and in keeping with their radical outlook, Thomas was educated at various progressive schools which nurtured independent thinking rather than adhering to a traditional curriculum. Perhaps because of this, at the age of seven Thomas was still barely able to read and write; so his father took it into his own hands to bring him up to speed.

The unsettled school career and frequent moves may later have made it difficult for Thomas to establish long term relationships, particularly with women. His mother prescribed a course in psychoanalysis. Hating his counsellor, who frequently fell asleep during sessions, Kuhn cured himself of his difficulties in establishing relationships by marrying Kathryn Muhs in 1948. Like his mother, Kathryn was a graduate of Vassar College. They had three children, Sarah, Elizabeth, and Nathaniel, before divorcing in 1978. Three years later Kuhn married Jehane Barton Burns.

His early literacy problems apart, Kuhn was an outstanding student with a particular interest in maths and physics. He was admitted to Harvard in 1940. America entered World War II during Kuhn’s second year as an undergraduate, and after gaining a BSc in physics in 1943 with the highest honours, Kuhn joined the Radio Research Laboratory, which had been set up to develop countermeasures to enemy radar systems. This took him initially to Britain and later into liberated France and Germany itself, to examine captured equipment first hand.

On his return to Harvard, Kuhn continued studying physics as the most convenient route to gaining a doctorate, which he achieved in 1949, although his commitment to physics was dwindling as his interest in philosophy was growing. While working on his PhD, he was invited to teach a course in the History of Science to undergraduates, and it was while preparing for this that he had the insight that was to inspire his most influential work.

One of the key moments in the development of his ideas was his study of Aristotle. The view of science at the time was that it is accumulative; so Kuhn went looking into Aristotle’s ancestral physics, expecting to find the foundations on which Galileo, Newton et al had later built. Instead, Kuhn was baffled to discover that Aristotle’s understanding of physics was, from a modern point of view, complete nonsense. Struggling to comprehend how someone so wrong could be so revered, Kuhn realised that in order to appreciate Aristotle he had to understand the context in which Aristotle had been working. In doing so, he drew a picture of science that was completely different to most contemporary analyses.

The Scientific Method, Historically Speaking

In the middle of the twentieth century the philosophy of science was almost exclusively focussed on defining the scientific method. The assumption was that science is an objective ideal method independent of human foibles, and if we could just describe its characteristics then everyone would have a template for doing proper science.

The debate was largely between the logical positivists and Karl Popper. Both sides took the view that science was a rational endeavour, and that scientists obediently followed where the evidence led them. Broadly speaking, the logical positivists stuck to the traditional view that science was the accumulation of facts and the refinement of mathematical models that accounted for those facts with ever-increasing accuracy. Their distinctive feature was they insisted that science should stick strictly to observable facts and avoid building theories not directly supported by those facts. Logical positivism advocated the ‘verification principle’ promoted by A.J. Ayer in Language, Truth and Logic. This demanded that anything that could not be supported by empirical evidence or strict logic was metaphysics and had no place in science (or indeed, anywhere else). One major problem – which in fairness the logical positivists were well aware of – is that no amount of empirical evidence (or logic) can prove a scientific claim. The classic example is that a million white swans do not prove that every swan is white. Popper’s innovation was to point out that it only takes one black swan to prove that the proposition ‘all swans are white’ is false. So the evidence could show you either what was only likely to be true, or what was definitely false. Therefore, as an endeavour seeking certainty, science should commit itself to trying to prove its own theories wrong. This is Popper’s principle of falsification.

The Structure of Kuhn’s Revolution

By looking at the historical evidence concerning science itself, Kuhn believed that he could see a pattern in the data (this is after all part of what physicists are trained to do). According to Kuhn, history showed that most scientific research, in whatever field of science, is guided by a set of principles and core beliefs about which there is a general consensus. The word Kuhn used for this guiding intellectual framework was ‘paradigm’. For instance, before Copernicus turned it upside down, Aristotle’s model of the universe, which put the Earth at its centre, was accepted for two thousand years. Some of the data was puzzling, and couldn’t easily be reconciled with this model, but scientists and mathematicians, most notably Ptolemy, worked within the paradigm to solve those puzzles. During that time, astronomers were able to plot and predict the positions of the heavenly bodies with an accuracy that is remarkable, especially given that later technological advances (not least the telescope) have shown the model to be demonstrably false; but for the scientific purposes of the time, Aristotle’s model worked. Working within the bounds of a paradigm is what Kuhn called ‘normal science’, and this is what these Aristotelian cosmologists were doing. In this way, the practise of medieval astronomers resembles the practice of the scientific method that most philosophers of science were trying to model. It is only in the rare occasions of scientific revolutions, when the data can absolutely not be made to fit the existing paradigm, that the paradigm itself changes. This is called ‘revolutionary science’ by Kuhn.

One of Kuhn’s early essays was called ‘The Essential Tension’ (1959). In it he discusses the conflicting pulls of the desire to innovate and the conservatism needed to do normal science. For every revolutionary Einstein, there are thousands of normal scientists who do the routine calculations that keep the scientific world ticking along. Most normal scientists are content to use a paradigm which for all current purposes works extremely well. Contrary to Popper’s recommendation, they don’t abandon a paradigm because they can’t fit a set of data into it: they may instead seek to modify the paradigm until the data fits it. A modern case is creating the ideas of dark matter and energy to fit galactic movement within the paradigm of Einstein’s General Relativity. Of course, there are also revolutionary scientists trying to develop new paradigms which aim to explain the same evidence in innovative ways. There are, for instance, many novel quantum theories which seek to incorporate gravity, of which String Theory and Loop Quantum Gravity are just two examples.

Among the most controversial aspects of Kuhn’s model of science, is his claim that different paradigms are ‘incommensurable’. That is to say, in extreme cases, there can be no meaningful dialogue between scientists who hold the different perspectives. That the same evidence can inspire different worldviews is often illustrated by the duck/rabbit illusion. The point Kuhn was making is that if you’re talking about a duck, you are going to make no sense to someone seeing a rabbit. String Theorists look at the universe and see eleven dimensions, whereas according to Loop Quantum Gravity, there are only four.

This raises another issue for which Kuhn’s paradigm model is criticised. How do you decide whether you are looking at a duck or a rabbit? The ‘theory-dependence of observation’ is this idea that exactly the same information can be interpreted in different ways. Kuhn argued that just as your worldview is influenced by your experience, so your scientific paradigm is determined in part by the education you’ve had. This led to accusations of relativism, which Kuhn tried to counter by saying that there are objective criteria for deciding between paradigmatic theories:

1. How accurately a theory agrees with the evidence.

2. It’s consistent within itself and with other accepted theories.

3. It should explain more than just the phenomenon it was designed to explain.

4. The simplest explanation is the best. (In other words, apply Occam’s Razor.)

5. It should make predictions that come true.

However, Kuhn had to concede that there is no objective way to establish which of those criteria is the most important, and so scientists would make their own mind up for subjective reasons. In choosing between competing theories, two scientists “fully committed to the same list of criteria for choice may nevertheless reach different conclusions.” Eventually though, according to Kuhn, a new, revolutionary model is found that most people settle down to developing, by using the new model to solve puzzles in the way of normal science.

The Reception of the Revolution

Many philosophers and physical scientists were initially sceptical, hostile even, to the depiction of scientists as normal people who held opinions and made decisions for idiosyncratic reasons. Social scientists, on the other hand, were inspired by The Structure of Scientific Revolutions to develop their discipline. Prior to publication, the most influential sociologist of science was Robert Merton, whose main focus had been on why scientific theories are rejected. After the Revolutions, sociologists largely turned to why scientific theories are believed.

In a way, Kuhn’s masterpiece was a product of exactly the sort of process it was describing. While ‘normal’ philosophers of science – the logical positivists and Popper – were working within a certain paradigm of what science was about, there was an accumulation of troubling anomalies. For instance, scientists such as Ludwik Fleck and Michael Polyani were pointing out that in their experience science didn’t actually work in the way that those philosophers assumed. Kuhn acknowledged his debt to both men. He also quoted the physicist Max Planck: “a new scientific truth does not triumph by convincing opponents and making them see the light, but rather because its opponents eventually die, and a new generation grows up that is familiar with it” (Scientific Autobiography and Other Papers, 1949).

For better or worse, Kuhn’s book changed the way science is viewed. Science is no longer straightforwardly an ideal method of gaining knowledge to which people should aspire; rather it is something shaped by ordinary, and a few extraordinary, people.

Kuhn spent much of his subsequent career elucidating and dealing with the fallout. It’s a major part of his legacy that now so does almost everyone else in the philosophy of science. “When reading the works of an important thinker,” he said, “look first for the apparent absurdities in the text and ask yourself how a sensible person could have written them” (‘The Essential Tension’). This is now what many sociologists and most philosophers of science are compelled to do.

Thomas Kuhn retired in 1991, age 69. In 1994 he was diagnosed with cancer of the throat and lungs. He died two years later, in Cambridge, Massachusetts, aged 73.

Will Bouwman is the author of Einstein on the Train and Other Stories: How to Make Sense of the Big Bang, Quantum Mechanics and Relativity.