What is the theme in The Anatomy of Melancholy by Robert Burton?

Melancholy is at the heart of this book. This work is a massive treatise on the malaise of melancholy. At least of the authors preceding Robert Burton had all too much experience with melancholy. Melancholy is the old name for an ailment contemporary psychologists call depression. There are diverse forms of this. There is a sense in which this work is simply an old medical document. As such it is about the history of medicine and psychology.