similarities and differences
Associations look arbitrarily for similarities between things and then try to analyse the basis for those similarities. These similarities, can however, be categorised. In his analysis of the human sciences Michel Foucault discovered four types of similarity which dominated thinking in the past.
 Michel Foucault, The Order of Things, an archaeology of the human science, New York, Vintage Books, 1973 (1966) pp. 17 ff.