The purpose of the study is to identify the main idea of the spontaneous associations concept proposed by Pasquale Rossi, an Italian researcher of the late 19th - early 20th centuries. Methods or methodology of the work. To study the P. Rossi’s concept, the following research methods of the theoretical analysis were applied, i.e. the historical and functional method that focused on studying the ideas of the Italian scientist, taking into account the logic of scientific development of that time; historical and genetic, involving consideration of the scientist’s scientific heritage, taking into account the social and historical conditions of the late 19th - early 20th centuries; as well as comparative and historical method aimed at comparing P. Rossi’s views with the views of some of his contemporaries, as well as particular provisions of modern psychological science. Results. The study contains a description of certain methodological errors found by P. Rossi in the concepts proposed by S. Sighele, G. Tarde, G. Le Bon. P. Rossi’s contribution to the development of collective psychology is characterized. The study shows the set of reasons that made collective psychology lose its status of an independent science that looks into social associations, specifies certain characteristics of the street crowd, proposed by Rossi, as well as provides his understanding of demopaedia as a new science of educating the masses. The aspects of P. Rossi’s research are noted, their further development being, according to modern scientists, quite promising for tackling topical social and psychological issues. Practical implications of the results. The conducted research seems relevant in the context of expanding the subject field of modern psychology of spontaneous social associations, as well as in developing the conceptual foundations of a systematic approach to this phenomenon.