IN Our Knowledge of the External World, Bertrand Russell makes a significant distinction between two kinds of infinity. One kind is illustrated by the progression from zero to 1, 2, 3, 4, 5, on to infinity; Russell calls this an infinite progression, and it is unlimited. The other idea is illustrated by the division of an interval between, say, one and two; first divide it into halves, then divide each of those halves, and so on infinitely. This is a compact series or an infinite class, and it is limited. The infinite progression and the infinite class are quite different ideas, and they have different philosophical uses. I suggest that a similar distinction may be made concerning literary forms, and that this distinction helps us to understand what is new about Ben Jonson's dramatic method. The distinction reverberates through seventeenth-century literature, I believe, but Jonson is especially interesting because he is somewhat of a pioneer.