In 1621, Robert Burton published a book called "The Anatomy of Melancholy," which may have been intended to be medical in nature, but wound up being more philosophical. Today, it can largely be read as a treatise on major depression–and it is only substantiated by Burton's own struggle with his melancholic temperament.
Here are some memorable lines:
I write of melancholy by being busy to avoid melancholy.
Melancholy… is the character of Mortality.
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