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A reflection on Karl Popper’s insights into the origins of scientific method and the pre-Socratics

If I was asked to teach an undergraduate course on Rationality 101, I would begin by introducing the students to the work of Karl Popper, especially Conjectures and Refutations, Objective Knowledge and The Open Society and Its Enemies.

Indeed, a good case could be made for having such a course consist entirely of acquainting undergraduates with the arguments in these three books and inducing them to think hard about them. Between them they cover principles vital to both natural and social science.

When I took first year philosophy almost 40 years ago, no such course was on offer. I remember an introductory course on Plato, which baffled me. The following year, I bought the superb Bollingen Plato: The Collected Dialogues, including the Letters, and grappled with Plato privately.

Interesting though that was, it did not convert me to Platonism. Popper, however, whose work I also read largely at my own initiative, did convert me to critical rationalism.

The decisive idea was the one he advanced in Conjectures and Refutations: interesting and productive beliefs are not to be had by either ‘revelation’ or deduction from ‘first principles’, but by generating and refuting conjectures.

By such means three things have developed within cognitive culture over time: constructive imagination, analytical acumen and corrigible knowledge – i.e. beliefs that can be checked and updated or discarded, based on critical inquiry.

A year or so before he died in 1994, Popper published The World of Parmenides: Essays on the Pre-Socratic Enlightenment, an attempt to dig down to the roots of the scientific method among the ‘natural philosophers’ preceding Plato and Aristotle.

Popper firmly believed that those two iconic figures had corrupted philosophy and brought scientific thinking to a halt. He believed it had originated, however, with Thales, Anaximander, Xenophanes, Heraclitus, Parmenides, Democritus and others, but had then been lost.

My own opinion in this regard differs from Popper’s. I believe that scientific thinking of just the kind he applauded continued well beyond Plato and Aristotle, peaking among Hellenistic scientists between the end of the 4th and the middle of the 2nd century BCE, then ground to a halt, less because of the influence of Plato or Aristotle than because the cognitive culture that had produced Euclid, Eratosthenes, Herophilus, Aristarchus, Archimedes and many others was smothered by Roman pragmatism. Nevertheless, Popper’s reflections on the pre-Socratics make fascinating reading for those interested in the origins of scientific thinking.

At the end of the introduction to The World of Parmenides, Popper described the era of the pre-Socratics as “the greatest and most inventive period in Greek philosophy; a period that came to an end with Aristotle’s dogmatic epistemology, and from which even the most recent philosophy can be said hardly to have recovered.”

Popper described the era of the pre-Socratics as “the greatest and most inventive period in Greek philosophy…”

Leaving aside the fact that this ignores the remarkable findings of the Hellenistic scientists, Popper’s book is interesting because of the fundamental cognitive breakthrough that he believes was made by the pre-Socratics. As he wrote, “The questions which the pre-Socratics tried to answer were primarily cosmological questions, but there were also questions of the theory of knowledge. It is my belief that philosophy must return to cosmology and to a simple theory of knowledge.”

The key to The World of Parmenides is Popper’s analysis of the cosmology of Parmenides and how, by setting out to understand and refute it, Leucippus and Democritus derived the theory of atomism. “There is a widespread belief,” Popper wrote, “somewhat remotely due, I think, to the influence of Francis Bacon, that one should study the problems of the theory of knowledge in connection with our knowledge of an orange rather than our knowledge of the cosmos. I dissent from this belief…[because] Western science – and there seems to be no other – did not start with collecting observations of oranges, but with bold theories about the world.”

Note the term ‘bold theories’, not ‘tall stories’. Popper is not concerned with competing myths here, but with conjectures that lend themselves to critical cross-examination, grounded in evidence and reasoning. He cites the strikingly counterintuitive and non-observational conjecture by Anaximander that the Earth was freely suspended in space and held stable by inertial forces, owing to its equidistance from all other heavenly bodies. Popper comments: “…this idea of Anaximander’s is one of the boldest, most revolutionary and most portentous ideas in the whole history of human thought. It made possible the theories of Aristarchus and Copernicus. But the step taken by Anaximander was even more difficult and audacious than [theirs] … To envisage the Earth as freely poised in mid-space and to say that it remains motionless because of its equidistance or equilibrium … is to anticipate to some extent even Newton’s idea of immaterial and invisible gravitational forces.”

One of the central problems stumbled upon by the pre-Socratics was that of change. What was the cosmos such that we could observe the mutability of things? How was such change possible at all? Parmenides postulated that there was, in fact, no change; that our perception of change was an illusion. This postulate was derived from his judgement that what is is, while what is not is not – from which it followed, he deduced, that there is no void and no room for movement or change. The cosmos is full: it is a single, dark, solid sphere, a ‘block universe’.

This strange conclusion, Popper observed, “may be described as the first hypothetico-deductive theory of the world. The atomists took it as such and asserted that it was refuted by experience, since motion does exist. Accepting the formal validity of Parmenides’ argument, they inferred from the falsity of his conclusion the falsity of his premise. But this meant that the nothing – the void or empty space – existed.”

“Consequently there was now no need to assume that ‘what is’ – the full, that which fills some space – had no parts; for its parts could now be separated by the void. Thus there are many parts, each of which is ‘full’: there are full particles in the world, separated by empty space, each of them being ‘full’, undivided, indivisible, and unchanging. Thus, what exists is atoms and the void. In this way, the atomists arrived at a theory of change – a theory that dominated scientific thought until 1900.”

Atomism was elaborated by Epicurus (341-270 BCE) into a philosophy of life. It isn’t clear how much of his thinking was derived from the hundred or so books written by Democritus, none of which has come down to us. But ‘Epicureanism’ became one of the enduring ethical and cosmological philosophies of the classical world.

The great Latin poem On the Nature of Things, by Lucretius (99-55 BCE) distilled the thinking of Epicurus into verse and counselled a view of reality freed from the terrors and superstitions encouraged by religion.

The rediscovery of atomism, Stephen Greenblatt argues, in The Swerve: How the Renaissance Began (2011), began to undermine the grip of religion on public affairs and moral discourse from the 16th century and to provide a foundation for the emergence of modern science in the 17th century. 

Little by little, classical atomism developed into modern atomism, with the discovery of the elements and their compounds, the realisation that atoms are not solid or unchangeable but chiefly consist of space themselves, and the investigation of atomic physics. The irony is that, conceptually, all this springs from the conjecture of Parmenides that change was an illusion – and its critical refutation by Leucippus and Democritus.

Popper did not venture into the arena of biology, but a similar story holds in that regard, of course. The bold conjecture by Charles Darwin that natural selection had driven a process of evolution and that the observable changes in the biological world were due to such selection pressures opened up the biosphere and the human past to inquiry in a way that no creation myth had ever done. 

The 20th century saw developments and refinements of this theory, with the integration of genetics into the picture and then the realisation, only 30 years or so ago, that evolution had proceeded not through a gradual, progressive process but via many changes and catastrophes of a quite haphazard nature – punctuated equilibrium. Little by little, our understanding had to be adjusted in the light of the refutation of assumptions or poor inferences embedded in the original conjecture.

Popper’s work helps to open up the thought processes by which such remarkable and fertile scientific conjectures have first emerged and then been refuted, reshaped and replaced to yield the scientific understanding of the cosmos and the biosphere that we now enjoy. That’s why a course in Rationality 101 might well feature his key books – not because he is an ‘authority’ or because he got everything right, but because he drew attention to the role and nature of free thinking and critical rationalism in a most illuminating way.

This article is part of our ‘The season for reason’ series of holiday reading focusing on rationalism and reason. It was originally published in the Winter 2016 edition of Australian Rationalist.


About Paul Monk

Dr Paul Monk is a public intellectual, poet, former senior intelligence analyst and consultant in applied cognitive science. He is the author of a dozen books, including 'The West in a Nutshell: Foundations, Fragilities, Futures' (2009), 'Dictators and Dangerous Ideas' (2018), his breakout book of poetry 'The Three Graces: Companionship, Discretion, Passion' (2022) and 'Thunder From the Silent Zone: Rethinking China' (2nd updated edition 2023). He is a fellow of the Institute for Law and Strategy (London and New York) and a fellow of the Rationalist Society of Australia.

One thought on “A reflection on Karl Popper’s insights into the origins of scientific method and the pre-Socratics

  1. Avatar photo Ric Streatfield says:

    An excellent article thanks Paul. It all seems to fit together beautifully. I’m very much an amateur at this, but your article links all my favorite ancient philosophers from Thales through to Epicurus….even one you left out. The ancient Indian naturalist philosopher Gotama (often called The Buddha) was apparently a contemporary of Socrates, according to Secular Buddhist scholar Stephen Batchelor. Batchelor suggests, in one of his books that Gotama may have attended Taxila University, up in the north-west of India at the time. I wonder whether at Taxila he may have been exposed to the thinking of the pre-Socratic Greek philosophers. I’m suggesting that because, around thirty to forty years ago I came across the ‘paticca samuppada’ where Gotama explains in great step-by-step detail to his assistant Ananda his insight called ‘Dependent co-Arising’. Except perhaps for Zen I think modern-day Buddhism has completely lost this absolute gem Gotama left us. Thanks again Ric

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