Ludwik Fleck (1896-1961): Polish physician and philosopher; sociologically-oriented approach to the study of the evolution of scientific and medical knowledge. Book: Entstehung und Entwicklung einer wissenschaftlichen Tatsache: Einfuehrung in die Lehre von Denkstil und Denkkollektiv (in German, 1925; translation: Genesis and Development of a Scientific Fact).

Fleck introduced the term 'thought collective': "People exist who can communicate with each other, i.e., who think somehow similarly, belong, so to say, to the same thought-group, and people exist who are completely unable to understand each other and communicate with each other, as if they belong to different thought-groups (thought-collectives)." "Every thought-collective considers that the people who do not belong to it are incompetent." "...cognition must be considered as a function of three components: it is a relation between the individual subject, the certain object and the given community of thinking (Denkkollektiv) within the subject acts; it works only when a certain style of thinking (Denkstil), originating in the given community is used."

Thomas Kuhn (1922-1996): scientist and philosopher; Book: The Structure of Scientific Revolutions. Science is not a steady, cumulative acquisition of knowledge; instead, science is a series of peaceful interludes punctuated by intellectually violent revolutions ('paradigm shift'); a scientific revolution is a noncumulative developmental episode in which an older paradigm is replaced in whole or in part by an incompatible new one; during periods of 'normal science', the primary task of scientists is to bring the accepted theory and fact into closer agreement.