Ludwik Fleck

From Encyclopedia of Scientonomy
Jump to navigation Jump to search

Ludwik Fleck (11 July 1896 – 5 June 1961) was a Polish-Jewish microbiologist, whose writings made an important early contribution to the historical philosophy and sociology of science. He was a pioneer in the social epistemology of science,1 and is seen as a significant influence on Thomas Kuhn’s Structure of Scientific Revolutions.2 Fleck developed a descriptive system of scientific communities, called thought-collectives (Denkkollektiv) with incommensurable thought-styles (Denkstil), and focused on the historical development and fallibility of “facts” as a result of faulty social constructions.

Fleck wrote the primary elements of his concept of thought-collectives and thought-styles in German before the Second World War in Lwów, Poland (now Lviv, Ukraine), notably in the 1935 book Genesis and Development of a Scientific Fact, and his 1936 paper The Problem of Epistemology. The invasion of Poland by Nazi Germany and Fleck’s capture in 1941 prevented further development of Fleck’s philosophy until after the war.

Fleck furtherer his ideas regarding the impossibility of universal scientific method in his paper Problems of the Science of Science published in 1946, and elaborated his thoughts about Gestalt psychology and incommensurability in his 1947 paper To Look, To See, to Know.

However Fleck only briefly extended his epistemological work after the war, working in Soviet-occupied Warsaw and focusing on his bacteriology and immunology work for this period of his life. He later emigrating to Israel to work in bacteriology and immunology until his death there in 1961.1 Only in 1979 did his works begin to receive major focus in English with Trenn’s translation of Genesis and Development of a Scientific Fact.

Historical Context

In terms of the sociology of science, Fleck was one of the earliest writers to suggest that scientific knowledge was culturally constructed. For this reason, along with his relative isolation from other philosophers of science, he is generally portrayed as ahead of his time.23

Fleck can be said to have been generally inspired by the work of early sociologists, like Durkheim and Lévy-Bruhl, although the extent of his knowledge of their work seems “superficial” at best,1 — Fleck devotes only a couple of pages to reviewing their argument in Genesis and Development of a Scientific Fact. He seems generally content to ignore the extent of their work and focus on the idea that “what actually thinks within a person is not the individual himself but his social community.” This idea is strongly echoed in Fleck's writing, both when he suggests that an individual takes their worldview, or thought-style from the teaching and induction to their community, and when he insists

Fleck's theory of the thought-style can be read as a response to Kant's universal synthetic a priori. Kant held that in order to learn anything from experience, we have to know something to experience it: some a priori knowledge that structures experience.1 For Kant, "the sensible world [...] is constructed by the human mind from a combination of sensory matter that we receive passively and a priori forms that are supplied by our cognitive faculties" — forms including perception of space, time, and causation.4 Without these, Kant would claim, the mind cannot interpret sensation into knowledge, and it therefore cannot think.1

These forms were supposedly universal and unchanging. Fleck agrees with Kant that human knowledge is constructed from some internalized knowledge like Kant's forms, and that form is necessary for the construction of sensation into knowledge, but, disagrees that any form is universal. Fleck instead sees the formal knowledge that constructs reality — one's thought-style — as the product of historical circumstances. Fleck would assert that the way a medieval monk, for example, sees the world through wholly different means than a theoretical physicist might. Taking from Durkheim's thesis on the sociology of thought, this formal style of thinking is the product of institutions and communities (thought-collectives) that an individual is part of.

Jonathan Harwood notes that Fleck, however, working mostly isolated, was far more radical in his approach. While Durkheim and other early sociologists of knowledge (especially Lévy-Bruhl) restricted themselves to the "beliefs of traditional societies," Fleck criticized this and extended his investigation to the influence of a thought-collective on the cognitive processes of individuals in all circumstances, including in the generation of scientific knowledge.5 In other words, Fleck extends the argument by asserting that any way by which members of a thought-collective see and think about the world is a sociological construction.1 As such Fleck is the first sociologist and philosopher to investigate the construction of scientific knowledge.

Major Contributions

Fleck on Thought-Collectives and Incommensurability

As explained above Fleck draws on Kant's conception of synthetic a priori forms to maintain that an empty mind would be incapable of thought or perception, and that knowledge must exist before a mind can experience. However Kant asserts that these a priori forms such as perception of space, time, and causation would be universal amongst all thinkers. Kant justifies this by noting that absolute knowledge of the world is possible to attain, such as Newtonian physics (which was accepted as certain in Kant's time). For certain knowledge to be attainable, Kant warrants, one's a priori forms must reflect a sensible world, and thus the forms Kant provides would universally reflect a consistent and sensible world-in-itself.4

Fleck reckons otherwise. Rather than a priori forms being the product of a sensible world-in-itself, Fleck states that different individuals in different communities and times possess distinct forms — different ways to view and organize phenomena, which he dubs a thought-style. Fleck likens changing between thought-styles to be similar to a kind of gestalt switch, insofar as an individual's entire understanding of perception and reality is based on the influence of various thought-styles. While Aristotelian physicians understand illness as an imbalance of humours, modern immunologists attribute the disease to an infection of bacteria or viruses. Fleck asserts that this is not a mere difference in explanation, but that these totally different manners of viewing the workings of reality.1

Rather than the product of a rationally ordered world, Fleck considers the thought-style a product of various thought-collectives. This includes (in Durkheimian fashion) institutions such as one's parents, school, and political associations, cultural background, and more pertinent in Fleck's research: a field of science. Through processes to induct members into each and the rituals that members undergo, certain fundamental knowledge is imparted which forms, for Fleck, that which Kant refers to as the synthetic a priori — the forms that are vital in constructing new knowledge.

Fleck asserts that a thought-style is not possessed alone by one individual, however, but that the thought-collective is an even “more stable and consistent” entity than the individual. As a style it is an emergent property of mutual understanding between the group, and if the group were to change so too would the thought-style.3 Fleck goes as far as to insist that without the effect of a collective, cognition is impossible for the individual, and they are left “blind and thoughtless” without a thought-style.6

For Fleck, and in contrast to Kuhn’s paradigms or Lakatos’s research programmes, no individual is the member of a single thought-collective,3 but “as a member of a political party, a social class, a nation, or even a race, he belongs to other collectives,”6 and moreover, the individual may move between collectives, and collectives may mutate via a process of “misunderstanding.”1 Fleck seems to disregard the view that a collective is a necessarily fixed or easily definable entity, having said that if the thought-collective were to change so too would the thought-style.

Fleck stresses that any thought-collective divides its social world into two parts, the esoteric and exoteric circles. The esoteric is composed of specialists, in more direct contact with the product of their work and a sub-collective which employs a denser set of terminology — a more particular bundle of facts that shapes the circle’s thought-style. The exoteric circle is alternatively composed of laymen, and demands less detailed understanding. Knowledge is delivered to the members of the exoteric circle by the intermediation of others. In a scientific thought-collective, the esoteric circle would be composed of scientists who speak in thick jargon in academic papers.1 The exoteric circle adopts some of that knowledge, diluted into simpler language and inevitable producing misunderstandings, when presented by authors in a simpler manner, and popularized.7

Fleck asserted that in a democratic collective such as modern scientific thought-collectives, the circles exist in a state of co-dependence — the exoteric circle relying on the esoteric for facts and advancement, while the esoteric depends on the exoteric for both economic and social validation. Importantly, individuals will belong to a few exoteric circles, and many esoteric circles, allowing the continuously circulation and mutation of facts.

Regarding incommensurability, Fleck takes a simplistic view at face value. Speaking in the language of their own thought-communities:

Scientists, philologists, theologians or cabbalists can perfectly communicate with each other within the limits of their collectives, but the communication between a physicist and a philologist is difficult, between a physicist and a theologian very difficult, and between a physicist and a cabbalist or mystic impossible.7

If all that scientists and theologians were to do was to speak “within the limits of their collectives,” then the thought-collectives would be incommensurable. This is not the end of the story, however. A scientist can create a platform of partial understanding, by appealing to the world or to simple examples, and attempt to teach a theologian the basis of the scientific thought-collective.1 Fleck dubs this process propaganda,7 and it too, like popularization of an idea from an esoteric to an exoteric circle, results in misunderstandings. Lastly, in a similar way that any member can move into the esoteric circle from the exoteric. Fleck refers to the process of initiation into the elite esoteric circle, via, for instance, the reading of prescribed textbooks and years of schooling,1 as necessary to produce the specialized thought-style to understand the esoteric circle.

Fleck on Scientific Change and Discovery

Fleck asserts that scientific change arises more frequently as a series of misunderstandings, as opposed to a logical progression towards "truth," and would reject that a "formal relation of logic exists between conceptions and evidence."3 Fleck avoids describing any universal requirements for the discovery of new facts, nor references the concept of a “method” in the way that Popper or Feyerabend might imagine such an idea. Fleck primarily speaks of the “discovery” of facts, rather than the justification of hypotheses as traditionally investigated. Despite his Kantian influence, Fleck neglects a divide between philosophical justification of hypotheses and psychological learning of facts. Yet given Fleck’s special focus on cognition and observation, and his basis in immunology, it is not surprising that he speaks in terms of “discoveries.”

Members of a thought-collective engage in different experiments, read different texts, and engage in discussions, and are furthermore involved in different thought-collectives beyond the one at hand. As such when they read each other's papers, misunderstandings in discovery, influence, and interpretation will arise. These misunderstandings generate new ideas and shape the facts of the thought-collective.1 Fleck’s understanding of incommensurability is important: “Strictly speaking, the receiver never understands the thought exactly in the way that the transmitter intended it to be understood,”3 such that in the processes of discovery, initiation into esoteric circle, and popularization and propaganda out of esoteric circles, no fact can possible remain entirely intact.

For Fleck, “discovery” is not a process of uncovering a universal truth, but rather is the result of the observation of individuals employing a thought-style, “discovering” knowledge that is permitted to exist in lieu of the premises of the thought-style. Fleck also was interested in the processes from which a thought-collective and -style are born. If a thought-style is “constructed” as Fleck says, when, by whom, and how is it constructed? What are the premises that restrict discoverable knowledge?

Fleck purports that a proto-idea lies at the basis of any thought-style, and provides persistent influence on the style and its facts over time. Fleck cites that modern atomic theory was developed step-by-step from Democritus’ atomist doctrine.3 Proto-ideas are initially generated (in the language of Fleck) as a spontaneous transposition of experience, in the form of analogies of a philosophical and spiritual nature.17 A proto-idea, says Fleck, becomes a subconscious guiding principle. Even if facts disintegrate the primitive assumptions of the proto-idea, it still conditions the pursuit of particular questions for the thought-collective.7

Before a thought-style exists to explain a kind of phenomena, or before an individual is inducted into the appropriate thought-collective to understand the phenomena, said "inexperienced person, [...] cannot 'see' — he 'looks'. He perceives at first only a 'chaos'.8 This chaos can be transposed into the foundation of a thought-style, to be elaborated on. For instance, Fleck cites that modern atomic theory was developed step-by-step from Democritus’ atomist doctrine.3 From the proto-idea of the atomists, modern atomic theory is fixed in position to ask about the combination and separation of atoms, their motions, and effects — and little else. This is strictly because that these presumptions lie in the basis of the thought-style, presumptions including the idea that inseparable particles exist, and hold in perfect mathematical relations to each other, and account for all matter. These presumptions and inherent guiding principles and relations are, according to Fleck, inherited from the pre-Socratic thought-style.

Fleck notes that contemporary members of a thought-collective will marvel at this “wisdom” and presume that their predecessors had a particularly strong sense of intuition. Fleck asserts that the reality is that these vague proto-ideas still hold a grip on the present-day community and shape the permitted pursuit of ideas, and the observational connections made (rather, the knowledge available to be discovered), such that it naturally seems obvious to have arrived at these observations.3 Modern atomic theorists arrived at the idea of indivisible, indestructible, fundamental and universal particles, just as the early Atomists did, not because of clever intuition but because that these presumptions were pre-set.

Fleck and Scientific Realism

In this sense Fleck is scientifically anti-realist. Scientific knowledge is constructed towards the aim of elaborating on what seems like intuitive wisdom, rather than towards absolute truth (even if members of a thought-collective might espouse this). Fleck supposes, hypothetically, that with a different proto-idea, such as one that constructs an analogy between “life” and “the ability to form shapes,” then crystals could be investigated as biological organisms. This would seem ridiculous to us because our thought-style and its underlying proto-ideas do not draw this relation, nor permit the pursuit of this, based on the groundwork of analogy in the style.7

After the establishment of the “guidelines” to a thought-style in its proto-ideas, facts will progress entirely irrationally according to Fleck. “In the history of scientific knowledge,” Fleck claims, “no formal relation of logic exists between conceptions and evidence. Evidence conforms to conceptions just as often as conceptions conform to evidence.” Fleck considers thought-styles to have a strong tenacity to resist change by evidence, citing primarily the detailed history of the scientific understanding of syphilis which he provides in The Genesis and Development of a Scientific Fact (his 1935 book).3


Fleck’s primary philosophical work was laid out in the mid-1930s, and while the reception of his papers was on the whole positive,1 the Second World War, and the invasion of Lwów in 1941 and Fleck’s capture by the Germans generally stunted the spread of his work — an English translation would not be available until 1979 with Genesis and Development of a Scientific Fact.

Fleck on the whole is frequently seen as a standout, peculiarly-informed precursor to future theories of the sociology of science — including features of incommensurability and historical a priori forms. Thomas Kuhn spoke positively of Fleck, considering him a predecessor and early adopter of many ideas that were present in the Structure of Scientific Revolutions. Only in Kuhn’s preface to Structure is Fleck’s work mentioned however, as “an essay that anticipated many of [Kuhn’s] own ideas.”9 Babette E. Babich suggests that Kuhn did not neglect, but rather intentionally avoided referencing Fleck in Structure proper in light of the Cold War political circumstances surrounding Structure’s publication.2

Fleck is most appreciated in circles of German philosophers and historians of science, also being seen as an early adopter of historical reconstruction, ala Kuhn, in the epistemology of science. As well, in France, Bruno Latour considers Fleck the founder of the sociology of science.1


Here are the works of Fleck included in the bibliographic records of this encyclopedia:

  • Fleck (1983): Fleck, Ludwik. (1983) Erfahrung und Tatsache [Cognition and Fact]. Suhrkamp.
  • Fleck (1979): Fleck, Ludwik. (1979) Genesis and Development of a Scientific Fact. University of Chicago Press.
  • Fleck (1936): Fleck, Ludwik. (1936) The Problem of Epistemology. In Cohen and Schnelle (Eds.) (1986), 79-112.
  • Fleck (1935b): Fleck, Ludwik. (1935) Entstehung und Entwicklung einer wissenschaftlichen Tatsache [Genesis and Development of Scientific Fact]. Schwabe.
  • Fleck (1935a): Fleck, Ludwik. (1935) Scientific Observation and Perception in General. In Cohen and Schnelle (Eds.) (1986), 59-78.
  • Fleck (1935c): Fleck, Ludwik. (1935) Zur Frage der Grundlagen der Medizinischen Erkenntnis [On the Question of the Fundamentals of Medical Knowledge]. Klinische Wochenschrift 14 (35), 1255-1259.

To add a bibliographic record by this author, enter the citation key below:


Citation keys normally include author names followed by the publication year in brackets. E.g. Aristotle (1984), Einstein, Podolsky, Rosen (1935), Musgrave and Pigden (2016), Kuhn (1970a), Lakatos and Musgrave (Eds.) (1970). If a record with that citation key already exists, you will be sent to a form to edit that page.

Related Topics

Role of Sociocultural Factors in Scientific Change
Role of Sociocultural Factors in Theory Acceptance
Static vs. Dynamic Methods
Sociocultural Factors
Scientific Change
Scientific Community


  1. a b c d e f g h i j k l m n o  Sady, Wojciech. (2016) Ludwik Fleck. In Zalta (Ed.) (2016). Retrieved from
  2. a b c  Babich, Babette. (2003) From Fleck's Denkstil to Kuhn's Paradigm: Conceptual Schemes and Incommensurability. International Studies in the Philosophy of Science 17 (1), 75-92.
  3. a b c d e f g h i  Fleck, Ludwik. (1979) Genesis and Development of a Scientific Fact. University of Chicago Press.
  4. a b  Rohlf, Michael. (2016) Immanuel Kant. In Zalta (Ed.) (2016). Retrieved from
  5. ^  Harwood, Jonathan. (1986) Review: Ludwik Fleck and the Sociology of Knowledge. Social Studies of Science 16 (1), 173-187.
  6. a b Fleck (1935) 
  7. a b c d e f  Fleck, Ludwik. (1936) The Problem of Epistemology. In Cohen and Schnelle (Eds.) (1986), 79-112.
  8. ^  Cohen, Robert S. and Schnelle, Thomas. (Eds.). (1986) Cognition and Fact: Materials on Ludwik Fleck. Springer Science & Business Media.
  9. ^  Kuhn, Thomas. (1962) The Structure of Scientific Revolutions. University of Chicago Press.