The Discarded Image is a series of lectures, later collected for print, in which C. S. Lewis told of the Medieval worldview, or the System, as he calls it, and its effect on literature of the time (and a bit afterwards - [[Literature/TheDivineComedy Dante]] features as an example). Very useful.
!! Some of the tropes discussed in this book:

* AllMythsAreTrue: Not true per se (you don't actually believe in Hermes and Athena, do you?), but the medievals tended to believe what they read, and what they had to read was ''eclectic''.
* ButIReadABookAboutIt: Lewis explains that in the Middle Ages there were no textbooks - bestiaries are not meant to teach about how animals actually behave, but how [[BeastFable men ought]], with a heavy dose of literary tradition that was chic to know. Same goes for maps and many other medieval writings. If you wanted a practical skill, you had to learn it from someone.
* DreamingTheTruth: If a medieval work contains a dream sequence, the dream will likely be of this sort.
* EarthIsTheCenterOfTheUniverse: Erm, yes and no. In the material order of things, sure. But in the ''spiritual'' order Earth is sort of the suburbs. (See Literature/TheSpaceTrilogy for a literary depiction)
* EpicCatalogue: The medievals loved catalogues of any sort, not always in epic poetry.
* TheFairFolk: Lewis mentions several medieval theories on what, exactly, they are.
* FourTemperamentEnsemble: The four temperaments are discussed in some detail, part of the definition of temperament being how the person handles '''anger'''. For instance, if you're an eleven year old and see your friend being bullied, you:
*** push the bully away, calling him some choice words, then focus on comforting your friend if you're Sanguine,
*** launch yourself at the bully with full intention of breaking nose if you're Choleric,
*** fret and obsess over what you should do, feel guilty about not doing it, possibly daydream later on about delivering an epic TheReasonYouSuckSpeech if you're Melancholic,
*** hang quietly in the background and help your friend clean themselves up later, while lending a sympathetic ear if you're Phlegmatic.
* ShoutOut: Since medieval culture was such a bookish one, these abounded.
* TropesAreTools: Tropes and figures are a sort of language - they mean things (has it changed?). The medievals didn't value originality of plot very much - they tried to tell edifying stories the best way possible.
* WesternZodiac: Astrology is also discussed, insomuch as it features in literature.