"he slept [much] better by book than by heart"

     "Pantagruel slept on a mattress, near a hatchway, holding a Greek text of Heliodorus in his hands.  That was his usual way, for he slept better by book than by heart [(trop mieulx par livre dormoit, que par cœur)]."

     Rabelais, Pantagruel (Gargantua et Pantagruel) IV.63, trans. Burton Raffel (New York & London:  W. W. Norton & Company, 1990), 512.  "Par cœur has the sense of « à la légère » [(lightly, rashly, thoughtlessly; unthinkingly, impulsively)]; cœur designates the seat of the memory" (Mireille Huchon and/or François Moreau, in the Pléiade edition of 1994, p. 1581n10).  "By-word.  In the Roman de la Rose, the lesson by heart (learned by ear) is already opposed  to the lesson by book" (Jacques Boulanger and/or Lucien Scheler in the Pléiade edition of 1955, p. 714n6, no citation).