John the carpenter, while admittedly short on brains, is probably the most sympathetic of the four major characters in "The Miller's Tale." After all, he's the only one who doesn't cheat or trick somebody. Ironically, though, he's also the one who suffers most in the course of the tale, being cheated on by his wife, tricked into spending the night cramped in tub hanging from the rafters of his house, taking a nasty tumble that likely breaks a few bones, and – as if all that weren't enough – being humiliated in front of the entire town.
Among the first things we learn about John is that, because he has married a much younger wife, he's constantly afraid that she'll cheat on him. Consequently, says the narrator, he's extremely jealous about Alisoun, keeping her on a tight leash. Yet John's actions actually contradict this characterization. When, for example, John hears Absolon serenading Alisoun outside their window, his only response is to ask her if she hears it too, and let the matter rest at that. Now, wouldn't a truly jealous husband be likely to punish the offending Don Juan, or the wife that incited the midnight serenade? Adding to our impression that John is in fact not the jealous type is his tolerance, even invitation of youthful male boarders like Nicholas into his home. Sorry, narrator, but John seems decidedly unconcerned about Alisoun's dealings with other men.
John doesn't seem so much jealous of Alisoun as devoted to her. Listening to Nicholas's forecast of a catastrophic flood, John's first concern is for his wife: "Allas my wif! / And shal she drenche? Allas, myn Alisoun!" (414-415). As he makes his preparations for the flood, he's almost brought to his knees in despair by the image of her drowning. His devotion to her, while somewhat misplaced, is decidedly endearing.
Yet there's another word some would use to describe John's devotion to Alisoun: stupid. And indeed, this is John's other main character trait. After all, he believes Nicholas's outlandish story about an imminent flood and obeys to the letter Nicholas's instructions about how to handle it, never for a moment thinking to question Nicholas's motives or character. One might also view as stupid John's decision to allow male boarders in his home despite the presence of a young, attractive wife. This is like inviting the fox into the henhouse, and were John more intellectually sharp, he'd know better.
A popular interpretation of "The Miller's Tale" reads the ending as meting out punishment to the various characters in proportion to their sins. Yet John upsets this calculus: his only sin is not being born with brains. In this, he is typical of the stereotypical portrayal of a lower-class person in estates satire. Yet John's character adds to this stereotype a sensitive, caring soul who sincerely worries about the welfare of those around him. His failure to spot Nicholas's treachery could be seen as stupid, but it could also be a sign of a trusting nature that comes from a lack of personal guile. In contrast to John, then, the treachery of the other characters shades from humorous to sinister – the metaphorical kicking of the puppy. His role, as a foil to the other three characters, may be John's most important one in "The Miller's Tale."