Among the growing number of domestic writings in Provence from the end of the Middle Ages, livres de raison comprised a heterogeneous corpus, combining elements of account books, family records, journals, and sometimes chronicles. Their writers, men and women from diverse social backgrounds, drew on complex and varying skills. While avoiding any teleology about the supposed “birth of the individual,” this article explores this heterogeneity to interrogate the specific textual and graphic procedures that reveal the subjective forms of the appropriation of the world and self in daily life. The livre de raison inscribes the individual within familial and social ties; at the same time, however, it constructs a space of personal writing where one could turn within oneself. Thus, behind its ordinary appearance and its collective vocation, the livre de raison established, on a daily basis, one's ordering of the world and reflective capacity.