Today, you write a book, someone just whether it can make money or not, and, if so, they print a run of it and sell them to people. The writer gets a fee and some percentage of the royalties.
I doubt that worked like that in the days of Chaucer, Milton, Alighieri, et cetera. Shakespeare had a theater and probably charged admission and whatnot, but how did the rest of them make money? Were they all independently wealthy?
Also, what about scientists, historians, mathematicians, and such in the days before there were universities with grants, commercial labs, and everything that supports them now?
I'm particularly interested in Europe prior to consumer economies and, preferably, prior to widespread literacy.
Many of them had wealthy patrons who commissioned their work. Others had positions in institutions like the Catholic Church.
To take some examples:
[1] Rosalyn Rossignol. Critical Companion to Chaucer: A Literary Reference to His Life and Work (New York: Facts on File, 2006). 551.
[2] Giulio Ferroni, Storia della Letteratura Italiana (Milan: Mondadori, 2006), 2:5.
[3] J.H. Plumb, The Italian Renaissance (Wilmington: Mariner Books, 1961), 165.
[4] Loewe Raphael, Ibn Gabirol (Cambridge: Cambridge University Press, 1989).