Prior to the publication of Kuhn's book, a number of ideas regarding the process of scientific investigation and discovery had already been proposed. Ludwik Fleck developed the first system of the sociology of scientific knowledge in his book "The Genesis and Development of a Scientific Fact" (1935). He claimed that the exchange of ideas led to the establishment of a thought collective, which, when developed sufficiently, served to separate the field into esoteric (professional) and exoteric (laymen) circles. Kuhn wrote the foreword to the 1979 edition of Fleck's book, noting that he read it in 1950 and was reassured that someone "saw in the history of science what I myself was finding there."