 Nineteenth century criminologists, including Taine 1887, Ferri 1884, Sighele 1891, and Le Bon 1895 investigated mental properties of crowds, such as impetuousness and irrationality. Tarde 1890 postulated mechanisms by which crowds acquire these characteristics, by way of the psychology of individuals and interactions among people. Durkheim 1894 challenged these explanations, arguing that such individualistic laws cannot be adequate to explain crowd psychology or other social phenomena. Durkheim argues that “social facts” are autonomous of individuals and have the power to constrain and affect their actions. In social ontology, Tarde is often seen as a representative of “individualism” and Durkheim of “holism” regarding the social world, and their positions remain a touchstone for contemporary debates (see  section 3).