This article provides an analysis of the only evidence that has — to the author’s knowledge — come down to us of the correspondence between the most authoritative 18th-century English grammarian Robert Lowth (1710–1787) and James Harris (1709–1780), author of the philosophical grammar Hermes (1751). The two extant letters uniquely provide insight into Lowth’s views on the pedagogical function of his grammar, on the innovatory aspect of his critical footnotes, and on some of the doubts and uncertainties he experienced while writing his grammar. All this adds to the radically different view of Lowth as a grammarian presented in The Bishop’s Grammar (Tieken-Boon van Ostade 2011), while the article also throws light on Lowth’s attempts at establishing a more private relationship with the author of one of the most important works within the wider 18th-century English grammatical tradition.