David Kaiser marks the 50th anniversary of the publication of Thomas Kuhn's best-selling The Structure of Scientific Revolutions (Nature 484, 164–165; 2012). It is only fair to point out that many of the same ideas had already been formulated by the Polish microbiologist and philosopher of science Ludwik Fleck in his 1935 study Genesis and Development of a Scientific Fact (translated into English in 1979). Kuhn acknowledged Fleck's contribution in the foreword to the first edition of his book, but this was ignored in the intense debate that followed its publication.

Fleck coined the term 'incommensurability' in 1927, which is still indispensable in discussions on Kuhn and the sociology of scientific knowledge. More on Fleck's theories and his influence on Kuhn's thinking can be found in the Stanford Encyclopedia of Philosophy (see http://go.nature.com/hpwnvd).