Franklin's humor is so different from that which students may be used to that they are sometimes baffled when teachers speak glowingly of the humor suffusing the Autobiography. While certainly present, the humor is marked by understatement and irony, modes of speech most effective when elaborate social rituals define "polite" conversational gambits. Thus the wit is often sly and soft, an undercurrent in the flow of language rather than the major channel.
Most humor in the Autobiography is found in Parts One and Three, but the dominant kinds of humor in these two parts differ. In Part One we find more often the confident burgher using himself as a target of his jokes ("my small Fund of Sense for such Performances was pretty well exhausted"), occasionally shaping his phrases so pointedly that we smile ("Keimer star'd like a Pig poisoned"), or employing the air of a worldly-wise philosopher, who flatters the reader by assuming the reader's appreciation of ironic jokes directed against men in general ("So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for every thing one has a mind to do."). Franklin includes several inherently funny scenes in this section (his own capitulation to the temptation to eat fish while sailing from Boston, or Keimer's inability to withstand the sight of a roast pig), but also makes effective humor from the inadequacies of polite speech (Ralph, deciding that teaching school was a profession which might later besmirch his name, "did me the honor to assume mine"). The humor in Part One is rich, varied, and relatively constant.
Part Three often includes amusing anecdotes, and particularly amusing things Franklin remembers having heard or said in former conversations. But this humor comes more in the form of set pieces. For example, Franklin is the butt of the joke when he tells of Whitefield's eloquence that moved him to contribute to the proposed Georgia orphanages in spite of his resolutions not to do so. But the climax of the reminiscence concerns another friend at the same service, who had taken the precaution to leave all his money at home, out of reach of Whitefield's exhortations. When he asked a Quaker friend to loan him enough to contribute, the Quaker replied, "At any other time, Friend Hopkinson, I would lend to thee freely; but not now, for thee seems to be out of thy right senses." Another self-contained anecdote is a mail carrier's description of Lord Loudoun's procrastination: "He is like St. George on the Signs, always on horseback, and never rides on." Franklin, in this third part, writes as an elderly man who enjoys recounting a good story, whoever originated it. As one who frequently schemed to obtain military funds from the reluctant Quaker Assembly, he especially enjoys the account of William Penn's secretary, who helped the crew fight off attackers when Quakers were first sailing to America. Later Penn reprimanded the man for engaging in violence, and he angrily replied, "But thee was willing enough that I should stay and help to fight the Ship when thee thought there was Danger. "
In whatever the section, Franklin's humor is never boisterous nor, at least in the Autobiography, bawdy. He remembered that brevity was the soul of wit, and made his humorous strokes quickly, deftly, and subtly — so subtly, in fact, that those unaccustomed to humor which makes demands on the intellect instead of the emotions sometimes miss it altogether.