'Splitters and lumpers': Samuel Johnson's tics, gesticulations and reverie revisited.

Medical diagnosis, even in psychiatry, has been made principally by 'splitters' and 'lumpers': those who separate categories of explanation and those who combine them. This paper, the text of an annual lecture delivered to a national British medical society, charts the detailed psychiatric diagnosis of one of Western civilization's most illustrious men of letters, Samuel Johnson, and explains how it was constructed in the last century. The aim is to provide a case study documenting the divergent methodologies of 'splitters' and 'lumpers' in practice.