"Diderot's study of cognitive deprivation as a way of understanding cognition itself is one of the most innovative moves in a century of intellectual innovation. Kate Tunstall's brilliant new translation and edition, accompanied by a lucid, witty and incisive essay that initiates the reader admirably into the complex problems raised by the Letter, will be a major resource for anyone wishing to understand core issues in the Enlightenment." - Terence Cave, Emeritus Research Fellow, St John's College, University of Oxford, UK