He knew nat Catoun, for his wit was rude. (Miller's Tale, I.3227)
Old John knew not Cato, for he had never been to school; the "Distichs" (closed couplets) of Cato were far and away the most popular elementary textbooks in schools during the early Middle Ages and beyond. They were prized not only as a means of teaching Latin but as a respository of valuable moral advice.
On Chaucer's use of Cato, see:
Richard Hazelton, 'Chaucer and Cato,' Speculum 35 (1960), 357-80 (Available on JSTOR for Harvard users).
The "Distichs" remained popular down through the end of the eighteenth century. Benjamin Franklin (who cites Cato once in Poor Richard's Almanac) probably studied the Distichs in Latin when he was a student at Boston Latin School, but he valued its moral content enough that he printed a translation:
The Cato of the Distichs was not Cato the Censor nor Cato Uticensis, though the work may have been attributed to the former by way of adding authority to the collection (just as collections of Middle English proverbs were attributed to King Alfred). Later the work was attributed to Dionysius Cato, of whom nothing further is known.
The Distichs often circulated with "monostichs" (one-line sentences), as a kind of prologue. The introductory monostichs and the distichs are here given in the edition by Wayland Johnson Chase, Univ. of Wisconsin Studies in the Social Sciences and History, Number 7, 1922 [WID Lc 25 42].
For an alternate edition, see: Distichis Catonis, ed. M. Boas and H.J. Botschuyver. Amsterdam. 1952 [PA6272.A2 1952; Widener LC 25.44].
For a slightly closer translation, see Minor Latin Poets, ed. J. Wight Duff and Arnold M. Duff, Loeb Library, Cambridge, MA. 1934 [PA 6156.A2 1934].