One of the usual jests about the study of philosophy is that you need a "day job," that philosophy doesn't undergird any remunerative employment. I recently saw a post on QUORA that constitutes a species of this genus. Someone asked, "What kind of jobs did philosophers like Rene Descartes and Spinoza do when they weren't philosophizing?" What was their day job? Descartes was well born, and at one point in his life he sold real estate, presumably inherited, and invested it in bonds, which allowed him to be comfortable for years thereafter. In later years, when he was famous for his philosophy, he supplemented his bond income with tutoring and, apparently, some military engineering. Spinoza was not as fortunate in his birth. He made a living grinding lenses. But it is worth noting that this activity was not unrelated to his philosophizing. Lenses, the microscope and the telescope, were at the time opening new worlds. A lens grinder was at a critical jun...