Tools of Characterization
See "Symbolism, Imagery, Allegory" for an explanation of how the clothing a pilgrim is wearing reveals things about his or her character.
See "Symbolism, Imagery, Allegory" for an explanation of how the physical appearance of the pilgrims reveals things about his or her character.
Certain trades in The Canterbury Tales lend themselves more easily to deception and cheating, and these are the trades practiced by the most loathsome pilgrims of the lot. Take the Summoner, for example. His portrait is unfavorable in general, so it makes sense that he makes his living by taking bribes from those summoned for excommunication. The same is true of the Pardoner, who makes a tidy profit on fake relics, or the Friar, who bilks poor widows out of their last dime to pay for his fancy clothes.
Some of what's going on here is estates satire and anticlericalism, both of which linked certain personality traits with certain occupations (see "In a Nutshell" and "Setting" for more about these traditions). Pilgrims who engage in what are more "honorable" occupations in the eyes of the poem, like the Tradesmen or Yeoman, generally have more neutral portraits. And we know that some pilgrims are ethically admirable merely because this is a part of their job description and we learn that they are a good Knight, Parson, or Plowman.
The activities in which pilgrims engage in their free time tell us a lot about their characters. The Miller is good at wrestling, and this fits very well with the impression we get that he's a very physical person. The Squire is good at writing poetry and playing the lute; he's a romantic with a sensitive soul, a fact confirmed when we learn that he spends all night tossing and turning over his various crushes. We learn a lot about how ethical various pilgrims are – and how poorly they fulfill their roles – if they engage in activities they probably shouldn't. The Friar enjoys hanging out in taverns, drinking, and carousing, so we know from this that he has immoderate physical desires (and is probably breaking his vows). The Monk engages in hunting and song-making competitions, preferring frivolous diversions to a hard life of religious discipline.
Because estates satire attached certain personality traits to certain social or occupational classes, we can make good assumptions about certain pilgrims based only on their social status. The Miller is low-class; the medieval stereotype of lower-class people is that they were intensely physical and earthy, but a little dim. Indeed, this is what we see in the Miller's portrait. On the other hand, noblemen were thought to take their obligations to help others and provide hospitality very seriously (noblesse oblige), a characteristic that the portraits of the Knight and Franklin confirm.