This article investigates the relation between a theorist’s theories and his daily life practices, using Émile Durkheim as an example. That theory and practice should be consistent seems not only scientifically proper but also morally right. Yet the concept of consistency conceals several different standards: consistency with one’s own theoretical arguments, consistency with outsiders’ judgments of oneself, and consistency within one’s arguments (and actions) across time and social space. Analysis of 750 pages of Durkheim’s letters shows that Durkheim lived a life consistent with and informed by his theories for most of his career. In his professional relations, his personal relations, and his political positions, Durkheim’s moral activity usually proceeds from his theoretical commitments. However, the death of his son in combat could not be theorized within the Durkheimian system, and it broke up this long stable pattern. The analysis concludes that under modern conditions, the issue of moral consistency relates closely to the general problem of solidarity and invites more complex theorization.