This chapter argues that trust and testimony acquire a significance in the work of Hume and his contemporaries that belies the relatively scant (and in Hume’s case, ambivalent) attention they devote to the subjects. Following Annette Baier, Steven Shapin, Martin Hollis, Guido Möllering, and John Hardwig, it suggests that trust, being fundamentally non-rational and social, is antithetical to the Cartesian picture of a lucid, private rationality. By enshrining trust as epistemologically constitutive, the Humean picture of communicative intelligence emerges as identifiably anti-Jacobin, the antitype of Rousseau’s picture of civic virtue as based upon transparency, perfect sympathy, and reason. The chapter proceeds to explore the ways in which the conflict between instrumental reason and trust that continues to exercise philosophers and economists today has its roots in the work of Hume, Reid, Smith, and other thinkers from this period.