Ideology, typically defined on a left-right spectrum, should provide a means of communication between elites and masses. After years of leftist party rule, have Brazilian voters internalized ideological divisions? Longitudinal surveys conducted from 2002 to 2006 reveal high nonresponse and instability in ideological self-identification. We find that the capacity to think ideologically is in part a function of political and social context. This capacity has real political consequences. A Heckman selection model reveals that those who refuse to take an ideological position or who exhibit high instability in self-identification tend to be latent rightists and to choose rightist presidential candidates. Moreover, they interpret the ideological spectrum differently from those who are more consistent in ideological self-placement. We thus make two contributions, showing how contextual factors influence ideological thinking and how low levels of ideological thinking affect the measurement of Brazilian public opinion.