coy,/Her greatest oath was only "By St. Loy!" (ll. 122-24)

Chaucer's choice of Madame Eglantine's oath to St. Loy is not random. St. Loy, the English rendering of St. Eligius, is a Bishop of Noyon who was known for having been the goldsmith for several of the Merovingian kings in France and was a courtier with particularly fine manners and clothes. Only later in life did he become concerned with the poor. Madame Eglantine's choice of patron saint is consistent with her behavior, described as "a courtly kind of grace,/a stately bearing fitting to her place" (ll. 144-45). Later, we learn that she has a brooch, which is inscribed with the phrase "Amor vincit omnia," or love defeats all—a concept common in the doctrine of courtly love, not in the Church that the Prioress represents.

The gap between the ideal and the real is much wider when Chaucer exercises his humor on the Monk, who should be quietly contemplating salvation in a monastery or ministering to the sick in his parish, but instead is

... a good man to horse;/Greyhounds he had, as swift as birds, to course [to hunt with him]. (ll. 193-94)

Chaucer describes a monk who has the trappings and behavior of a wealthy landowner—a horse, greyhounds to hunt with—that are antithetical to his position in the Church, which calls for good works rather than good hunting.

The Monk not only engages in unseemly behavior, but he also wears clothes to which he is not entitled as part of the religious establishment, going so far as to close his hood with a "wrought-gold cunningly fashioned pin;/Into a lover's knot it seemed to pass" (ll. 200-01), an ornament that would be strictly forbidden by his order and made worse by its "lover's knot." Another telling sign that the Monk has abandoned his calling is in Chaucer's description of his head, which "was bald and shone like a looking- glass" (l. 203), another violation of his order which would have required a tonsure.

With few exceptions among the pilgrims—the Knight, the Clerk of Oxford, the Knight's Squire (son), the Franklin—Chaucer finds significant gaps between the ideal and real in the personalities of the pilgrims, gaps that he explores with both gentle humor and biting satire, and in this, Chaucer's portraits create a montage of England in the Middle Ages.

The characters who journey together to Canterbury are an irreverent bunch, despite many of them being in religious orders.

Like all good humorists, Chaucer uses hyperbole or exaggeration to make us laugh. His evil clergy are not simply a little bit evil: they can be jaw-droppingly bad. One example is the Pardoner. This man has no shame whatsoever in his unrepentant bid to rake in as much money as he possibly can selling indulgences (pardons for sins) and pocketing as much of the money he can rather than giving it to the church. He openly tells of how he has weighted a brass cross with stones so he can pass it off as made of gold and says that his supposed saints' relics are merely pig bones. He even tries to sell indulgences to his fellow travelers, breaking the rules of the journey. There seems to be no depth too low for him to sink, and we laugh both at his audacity and at the slippage between what he is supposed to represent (a holy church) and his greedy, lying, cheating, low-life behavior.

Likewise, there is a certain ideal of a wife (as loving, submissive, and obedient) that the Wife of Bath not only violates but violates to such a degree that we again can't help laughing. She openly expresses that she married older men for money, not love, and quickly got control of the relationships during her first four marriages. Rather than being submissive and kind, she is feisty, manipulative, and difficult, psychologically tormenting her husbands into doing her bidding until she gets her comeuppance with the fifth and final one.

Such characters are so outrageously over-the-top that we can't help but laugh.

Chaucer juxtaposes the idealized public masks and true inner identities of these characters to a humorous effect. Generally, the more "noble" a pilgrim is, the more corrupt they are, though this is not always so.

For example, the Pardoner is an employee of the Church, selling indulgences to people so their sins can be forgiven and their time in purgatory allegedly lessened. However, he is a shady figure, pocketing the donations he receives which are supposed to go to the Church and making money by presenting peasants with fake relics. His behavior hints that he may also be homosexual, which the Church views as sinful, so it is clear that the Pardoner is not devout.

The Friar is supposed to live as a beggar and serve the poor. However, he is presented as lecherous, often having to find a way to marry off the young girls he seduces and impregnates. Even though he is supposed to gather alms for the poor, he is a man who prefers to take bribes.

Geoffrey Chaucer inserts himself into his masterpiece, The Canterbury Tales, as the narrator. In general, Chaucer doesn't have much of an active function in the poem itself, and his primary purpose is to observe and describe the other characters and report their tales (Chaucer does tell a few tales of his own, but the first is interrupted and criticized heavily, so it's clear the author isn't afraid of making fun of his status as a poet).

By inserting himself into his own poem, Chaucer subtly asserts that he directly observed everything he reports, a claim that lends extra credence to his narrative. Additionally, by separating himself from the characters during most of the tale-telling, Chaucer is also able to separate himself from their lewd and inappropriate stories. Many of the tales are bawdy even by contemporary standards, and so they likely would have offended audiences in the Middle Ages. By positioning himself as a passive observer of the action, Chaucer skillfully avoids blame or criticism for the inappropriate aspects of his poetry. We can almost imagine Chaucer speaking in his own defense, saying, "I didn't come up with this stuff! I'm just telling you what I heard!"  

Chaucer uses low comedy, involving physical, bawdy humor, in The Canterbury Tales. A prime example of this is "The Miller's Tale."

In this tale, the beautiful Alisoun is married to an older man, John the Carpenter. However, she is in love with Nicholas. In order to sleep together, she and Nicholas convince John that a flood is coming and persuade him to spend the night suspended in a basket. They take advantage of his foolishness to head for his bed for some lovemaking.

Meanwhile, Absolon, who is in love with Alisoun, comes to her window wanting a kiss. She presents her rear end rather than her face. That is an example of low, bawdy, physical humor. When Absolon realizes he has been laughed at and has kissed her rear end, he decides to get revenge by searing her with a red-hot iron. He comes to kiss her again, but this time Nicholas sticks his rear end out the window and farts in Absolon's face, another example of low humor. Absolon gets his revenge on Nicholas by using the hot poker. John, hearing Nicholas's screams for water, thinks the flood is coming and cuts the rope keeping his basket hanging. He crashes to the ground, and the villagers jeer at him as a fool.

None of this humor is subtle or sophisticated. It relies on our ability to laugh at physical pain and humiliation and to side with the aggressor who is cruelly tricking someone else. We might laugh just because we like someone being made a fool of, or, because it is so over-the-top, we still might laugh in spite of ourselves at the general absurdity of the situation.

Another example of bawdy humor is "The Reeve's Tale," where John and Aleyn get revenge on the crooked miller by moving a cradle so that the drunken miller's wife gets into bed with John by mistake. John immediately has sex with her, and John and Aleyn end up beating up the miller.

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. 

The main sources in The Canterbury Tales comes from the different aspects of irony used by Chaucer throughout the text. Chaucer uses verbal irony, situational irony, and dramatic irony in the text. It is this use of irony that provides the main source of humor throughout the text.

For example, in "The Pardoner's Tale", the priest constantly advises against the avarice (or greed). But, instead of taking his own advice, he is guilty of avarice. By allowing people to buy pardons and relics from him, the priest is lining his own pockets. This is an example of situational irony. Situational irony exists when the opposite of what is expected to happen happens.

Another example of irony in the story exists, again, in "The Pardoner's Tale". Here, the irony depicted is one of dramatic irony. The three thieves, on a quest for Death, find a bag of money. Each one decides that it would be in their favor to not have to split the wealth three ways. The men make plans to do away with another. In the end, all men die. This is an example of dramatic irony given the reader knows more about what is going to happen than the characters involved. The reader recognizes that when one seeks out death, the person will find it.

Your question gets to an ongoing debate among scholars of The Canterbury Tales with respect to the persona of Chaucer the Pilgrim and Chaucer the Poet. Is the Pilgrim an observant narrator but not particularly bright, or is he, like Chaucer himself, an astute judge of character whose descriptions of his fellow pilgrims are meant to be highly ironic because they depict the difference between the ideal and the actual? The tension between what seems to be and what is, after all, creates the humor in the poem.

If we look closely at a few observations Chaucer the Pilgrim makes, we will see that he is indeed a naïve and limited observer, but in the service of comedy and realism, the observer unfailingly focuses on the pilgrims' attributes that tell us where they are on the spectrum of the ideal and the actual.

When the observer describes the Prioress, for example, he notes that

Her greatest oath was but by St. Loy; and she was called Madame Eglantine. (General Prologue: 120-121)

Chaucer the Pilgrim is clearly entranced by the Prioress, but he mentions two attributes that, to a careful listener or reader, cast some doubts on the Prioress's devotion to her duties. First, her oath to St. Loy, which is short for St. Eligius, is to a saint who began life as a goldsmith and who became famous for his intricate jewelry designs. Later in life, he joined the Church and was canonized, but it is fitting that the Prioress, who appears more secular than religious, should choose St. Loy rather than, say, St. Jerome, to swear by. Second, a Prioress would not be using oaths, even mild ones, under any circumstances. Third, a Prioress would have adopted a religious name, most likely from the Bible, and would not have the title "Madame Eglantine." All of these details, which depict the worldliness of the Prioress, are simply recorded by Chaucer the Pilgrim to the delight of the listeners or readers, who understand that Chaucer the Poet is gently satirizing a woman whose secular attributes exceed her religious ones.

The portrait of the Friar, one of the most damning in the General Prologue, provides another example of Chaucer the Pilgrim carefully recording the Friar's history but failing to recognize the irony and humor embedded in his observation. The Friar, described as a "wantowne and a merye" (a pleasure loving and merry fellow), belongs to the most elegant of orders of Friars and has

So much of social graces and elegant language,/He had made very many a marriage/Of young women at his own cost. (General Prologue:211-213)

Chaucer the Pilgrim records this information as if with a recorder or video camera and, true to his naivete, fails to recognize that the pleasure-loving Friar is most likely marrying off his lovers before their pregnancies are noticeable. What appears to be an act of generosity to the observer is an act that confirms the Friar's corruption—there is irony in Chaucer the Pilgrim being blissfully unaware of the Friar's reality and irony in the portrait of such a corrupt representative of the Church.

Chaucer the Pilgrim, then, is depicted as a well-meaning, accurate observer, but one who continually misses the import of his observations and unknowingly creates the irony and humor that infuse the poem. Chaucer the Poet has created the perfect foil for his brand of both gentle and biting satire, which he uses to depict a wide spectrum of medieval English society.

Chaucer's Canterbury Tales are indeed a great example of humor not only for his time period (14th century), but also for audiences today because each tale brings a sense of truth to society. In Chaucer's day, poetry was thought to only be understood by the rich or elite because it was only written in Latin or Italian. But, by writing these tales in English, Chaucer opened the door for all classifications of life to be able to read poetry and enjoy it. "The book...gives a rich, intricate tapestry of medieval social life, combining elements of all classes, from nobles to workers, from priests and nuns to drunkards and thieves" (enotes Canterbury intro). Capturing the various human temperament of the time holds a great interest to audiences still today. And, because Chaucer wrote the tales to entertain, his use of satire and irony make many of the tales comical.

As the pilgrims embark on their journey to Canterbury, Chaucer provides his characters with individual tales focusing on Christianity. This provides humor because it allows for the faults to be seen in both formalized religion as well as the people who follow it.  Chaucer contrasts many of the characters and their views such as the Knight and the Franklin telling a tale of love and forgiveness to the Wife of Bath who twist the Bible verses to suit her promiscuous behavior to the Miller's tale with the using flatulence as a weapon of revenge. Much of what is found in the tales could be found in comedies today.