Logo ETH Zurich
Logo University of Zurich
Logo Zurich University of the Arts


“One must not forget that there exists no fully completed science but only one that is becoming.”

Ludwik Fleck, “On the crisis of ‘reality’” (1929)

Ludwik Fleck (1896-1961) is considered a pioneer of modern research into science. He is the originator of such concepts as Denkstil [= “thought style”] and Denkkollektiv [= “thought collective”], terms currently in use. Nevertheless, the monograph he published in 1935 with Schwabe Verlag in Basel, Entstehung und Entwicklung einer wissenschaftlichen Tatsache [Genesis and Development of a Scientific Fact, Chicago 1979], went unnoticed for decades, as did his shorter epistemological works and writings on the sociology of knowledge. It was not until Thomas S. Kuhn published a brief tribute to Fleck in the preface to The Structure of Scientific Revolutions (Chicago 1962), his bestselling work on the history of science, that a belated reception of Fleck’s work began. From the late 1980s on recognition of his significance grew steadily and ultimately earned Fleck’s work its current status as a classic. Despite his posthumous renown as a historian of science, however, during his lifetime Fleck was a practicing physician and natural scientist. As a researcher and head of a laboratory he participated successfully in work in the field of bacteriology and serology, and the number of his publications in medicine and the natural sciences, published in respected medical journals, far outweighs those in the field of reflection on knowledge.
Ludwik Fleck's life as a Jewish scientist in the 20th century took him through the university as well as the ghetto and the concentration camp, through the Europe of world wars and totalitarian systems, and ultimately to Israel.

Fleck’s main writings on the theory of science are available in English as:
Fleck, Ludwik, Genesis and Development of a Scientific Fact, edited  by Thaddeus J. Trenn and Robert K. Merton, translated by Fred Bradley and Thaddeus J. Trenn, foreword by Thomas S. Kuhn.  Chicago: University of Chicago Press, 1979.
Fleck, Ludwik (1983), Cognition and Fact. Materials on Ludwik Fleck, edited by Robert S. Cohen and Thomas Schnelle, Dordrecht: Reidel, 1986 (Boston Studies in the Philosophy of Science, Vol. 87).

More about Ludwik Fleck (W. Sady, 2012)


11.7.1896 Ludwik Fleck is born in Lemberg (Lvov), at the time part of the Austro-Hungarian Dual Monarchy, to Polish-Jewish parents.
1914-18 Studies medicine and performs military service during First World War; earns doctoral degree in general medicine.
1920 Holds assistanceships in academic research (infectious diseases).
1923 Marries Ernestina Waldmann.
1924 Birth of son, Ryszard Ariel.
1923-27 Directs bacteriological laboratory at the General Hospital in Lemberg while at the same time establishing a private bacteriological laboratory.
1928-35 Directs bacteriological laboratory of local health insurer in Lemberg.
1935 Following dismissal as Director continues to work in his own private laboratory; publishes monograph entitled Entstehung und Entwicklung einer wissenschaftlichen Tatsache [= “Genesis and Development of a Scientific Fact”].
1939 Soviet occupation of Lemberg; Fleck returns to the university and becomes a lecturer in microbiology.
1941 German attack on the Soviet Union; Fleck and his family are deported to the Jewish ghetto in Lemberg.
1943 Imprisonment in Auschwitz concentration camp; Fleck works in the serological laboratory at the Hygiene Institute run by the Waffen-SS.
1944 Fleck is deported to Buchenwald concentration camp; works in the laboratory producing a vaccine against spotted fever, or typhus.
1945 Liberated from Buchenwald; returns to Poland; appointed Director of the Department of Medical Microbiology at the University of Lublin.
1946 Completes “habilitation” work, enabling him to be granted a full professorship.
1950 Appointed Full Professor of Microbiology at the University of Lublin.
1954 Inducted into the Polish Academy of Sciences.
1955 Awarded Officer’s Cross of the Order of Poland Reborn; as a member of the Board of the Academy of Sciences, Fleck develops its medical section.
1956 Suffers heart attack and is diagnosed with lymphatic cancer.
1957 Fleck and his wife emigrate to Israel, where he is appointed Director of the Institute for Experimental Pathology at the Israel Institute for Biological Research in Ness Ziona.
1959 Appointed Visiting Professor of Microbiology at Hebrew University in Jerusalem.
5.6.1961 Ludwik Fleck dies of a heart attack in Ness Ziona.