6 ideas
In medieval literate culture a book was not a replacement for memory but a cue for it: one read in order to lay the text down in one's own mind, where it could be recalled and used without the page. Education therefore judged a person by what they had stored and could draw out at will, not by what they could look up.
Trained memory worked as a storehouse of divided, located pieces (a thesaurus or cella) that the thinker went through to gather material. Composing (inventio) meant taking a route through these stored places and pulling items together, so invention was a kind of retrieval and recombination rather than creation from nothing.
Aquinas, glossing Aristotle and Cicero, lays out four rules for better remembering. First, attach what you want to remember to fitting, somewhat unusual images, because the mind holds on to sensory likenesses better than bare abstractions. Second, set it in a deliberate order so that one item leads to the next; third, attend to it with care and emotional engagement; and fourth, rehearse it often.
Long material gets memorized by breaking it into short units a person can take in at a glance and tagging each with a distinct cue, such as numbers, alphabetical keys, or vivid marginal images. Features of the medieval page like rubrics, initials, and grotesque decorations served in part as memory handles, not only as ornament.
Medieval writers described memorized reading as eating and chewing the cud (ruminatio): taking in the text, then murmuring and turning it over repeatedly until it became part of the reader's own moral substance. From this angle, reading changes the self by absorption rather than simply transferring information.
Trained memory was classed under prudence because judgment depends on bringing past experiences and exemplars to bear on present decisions. A well-furnished memory was therefore a sign of moral character, and the cultivation of memory was treated as the formation of a person capable of wise action.