It becomes clear as the play progresses that this play is not about the four humours believed to give medieval man his character so much as about human folly. Jonson himself in the prologue of the play writes that the focus of the play and of the comedy is "deeds and language such as men do use." In addition, the prologue states that his comedy plans to "sport with human follies, not with crimes." The play thus takes as the source of its comedy the stupidity of human nature rather than using the theory of the four humours as its basis. In this play it is clear that for Jonson the humours can be taken to mean the caricatured manners of people so that the comedy of humours is actually just another way of saying this play is a comedy of manners. Note for example Knowell's opening speech where he reflects on his son's liking for poetry and how he shared that liking in his youth as well:
Myself was once a student; and, indeed,
Fed with the self-same humour he is now,
Dreaming on nought but idle poetry,
That fruitless and unprofitable art,
Good unto none, but least to the professors,
Which then I thought the mistress of all knowledge:
But since, time and the truth have waked my judgement,
And reason taught me better to distinguish
The vain from th'useful learnings.
Age and cynicism are captured perfectly in Knowell's comments as he looks back and sees poetry as "fruitless and unprofitable." Jonson is mocking attitudes to education and the arts and Knowell's inability to wean his son from his liking of poetry is one of the sources of humour in this comedy.