It is frequently maintained that rationalism is something other than an 'ism' of International Relations. Inspired by critical theory but using quantitative survey data, this article takes issue with that notion, arguing that rationalist work - with its emphasis on interests, institutions, and information - has a distinct logic of individualistic utilitarianism. It therefore exhibits all of the subjective biases of other 'isms', defining both the answers and the very questions that are asked. Using data from the 2011 TRIP survey, I show that those substantive commitments reveal themselves in the economic ideology of those who make rationalist assumptions in their work. Parallel to a view of international relations in which egoistic units seek material gains, rationalists identify as economic libertarians at a much higher rate than non-rationalists. All of this suggests that rationalists have an unacknowledged and unconscious bias in their scholarship that threatens the positivistic epistemology to which most claim to be committed.
