Nearly every writer on detective fiction has resorted to analogy as an aid to definition or explanation. The analogies have varied considerably, from religious ritual to the minuet, but three large groups have been most prominent: games, logic and mathematics, and other literary forms. The analogies to games range from card games and jigsaw and crossword puzzles to football and other sports. R. Austin Freeman called the genre "an exhibition of mental gymnastics," and he was joined by Willard Huntington Wright, who not only described detective fiction as "a kind of intellectual game ... a sporting event," but even as "a complicated and extended puzzle cast in fictional form." Numerous other critics have followed this line. Julian Symons' characterization of such fiction as "an exercise in logic" and Dorothy Sayers' statement that in "its severest form, the mystery story is a pure analytical exercise" are typical of the second group. Often, however, blame is implied by such analogies, as in Mary McCarthy's view that the characters in such stories are "about as real as the A and B of the algebra problems"; on the other hand, John Leonard uses the same analogy to defend Christie specifically: her stories "were elegant, as a balanced equation is elegant. Who complains about the x, or any other quantity, in an equation?" Francis Wyndham even coined the phrase "animated algebra" to characterize Christie's work: "Agatha Christie writes animated algebra. She dares us to solve a basic equation buried beneath a proliferation of irrelevancies."

The third group of analogies is, as might be expected, the largest, for the tendency to find resemblances between detective fiction and other forms of literature is natural; what is unusual is the forms most often chosen. As early as 1913 Carolyn Wells found an equivalent to detective fiction in the fixed forms of verse: the sonnet and the French forms, such as the triolet, the sestina and the rondeaux. Others have agreed, among them Sayers, C. Day Lewis, Richard Lockridge, Michael Gilbert, Hillary Waugh and John Cawelti, particularly as to the sonnet. Waugh's statement that "the mystery is to the novel what the sonnet is to poetry" is matched by Cawelti's "The formula of the classical detective story is as rigid and formalistic as that of the sonnet." Michael Gilbert uses a double analogy to differentiate between the classic detective story and the thriller: "The detective story is the sonnet. It is precise, neat, satisfyingly symmetrical, constrained, but sustained, by the nicety of its form.... The thriller is the ode. It has no formal rules at all. It has no precise framework." Among other literary forms to which detective fiction has been compared are the medieval morality play, Renaissance pastoral, Restoration comedy, the fairy tale, the comedy of manners and, of course, melodrama.

The point of most of these analogies, of whichever group, is the sense that form, pattern and even rules govern detective fiction. The attitude is summed up by Dorothy B. Hughes: "The mystery novel, like the theatrical play or the sonnet, is contained within a prescribed pattern. The writer may wander a bit but not far, not and stay within the form." One may dislike the form, or the work of a specific writer using it, but one cannot help realizing that it is present; even Georges Simenon's comment on his detestation of Christie - "It's not literature, it's embroidery." - implies an awareness of an underlying pattern. . .