Every gesture of the daily life of an individual is structured by a series of social constraints leading it to conform to an existing social order. This Sociograph examines how the most intimate of these aspects, the way an individual thinks, is socially framed. Using the data of the Swiss Household Panel, the work analyzes to what extent the fact of becoming a union member is capable of influencing a series of job, political and social attitudes. After a brief characterization of the Swiss union landscape and an analysis of the declining trend of union density in Switzerland, the reader is led to consider the methodological issues to take into account when trying to tease out causal effects from observational data. By exploiting the advantages of a panel data approach, the results reveal whether the attitudinal differences existing between union members and non-members can be traced back to a causal effect of union membership or whether they are to be attributed to pre-existing differences between the two groups. If a causal effect of union membership is indeed there, it is shown that the nature of the mechanisms explaining its appearance varies according to the sector of activity, to the profile of the individual and to the attitude taken into account.