| Quote #1
He knew nat Catoun, for his wit was rude.
By calling John's wit "rude," this quote is not just saying that he's stupid, but that he's unlearned. That is, he does not have the schooling that people like Nicholas and Absolon do, which fills one's head with the sayings of learned philosophers like Cato.
| Quote #2
He knew nat Catoun, for his wit was rude,
The Greek philosopher Cato said that like should wed like. If people were too different, went the thinking, they would not be compatible. An misogynist "spin" on the saying claimed that a young woman was sure to be lustful and would not be satisfied by the sexual vigor of an older man. In either case, John is foolish for marrying Alisoun.
| Quote #3
A clerk hath litherly biset his while,
A clerk has an educational advantage over a carpenter; as we saw a few lines earlier, clerks are knowledgeable in the teachings of philosophers. The idea was that these teachings would provide one with life experience that one could not otherwise gain.