In the late 19th century, a comprehensive semantics of crowds emerged in European social theory, dominated in particular by Gustave Le Bon and Gabriel Tarde. This article extracts two essential, but widely neglected, sociological arguments from this semantics. First, the idea that irrationality is intrinsic to society and, second, the claim that individuality is plastic rather than constitutive. By following the destiny of this semantics in its American reception, the article demonstrates how American scholars soon transformed the conception of crowds. (...) Most importantly, the theoretical cornerstone of the European semantics, the notion of suggestion, was severely challenged in the USA. It is argued that this rejection of the suggestion doctrine paved the way for a distinctive American approach to crowds and collective behaviour in which the early European emphasis on irrationality was ignored and crowds were analysed as rational entities. This may have relieved the discomfort of irrationality but it is also entirely disposed of what were in fact crucial sociological insights. The article recalls the semantics of crowds in order to evoke an early branch of social theory that still contains a provocative gesture. (shrink)