Much of Chaucer's humor in The Canterbury Tales comes from irony. Opposition is the essence of irony, and Chaucer presents opposites to create humor.
For instance, Chaucer's Friar is not like what the average person might expect a friar to be like:
He'd fixed up many a marriage, giving each
Of his young women what he could afford her.
He was a noble pillar to his order.
In other words, after having affairs with women, he would find them husbands and pay them what he could. He obviously was not really a "noble pillar to his order."
Chaucer accomplishes this irony by using a narrator who is good natured and a bit naive. The narrator assumes the friar is a nice guy for finding women he has had affairs with husbands, not realizing that the Friar is covering and protecting himself by doing so.