The chiasm, or chiastic structure, is a pattern of organizing ideas in a narrative that was commonly used in ancient Hebrew scripture. Put simply, a chiasm follows the following structure: A B C D C’ B’ A’
The idea or action presented in A is repeated with a slight variance in A’. The idea or action presented in B is repeated with a slight variance in B’. The idea at the center often has no corollary and it’s uniqueness in the story or poem grants it greater emphasis. Here’s an example (taken from a post on Peter Leithart’s blog) of a chiasm found in Genesis 17:
A. Abram is “99 years old”, v 1a
B. Yahweh appears, v 1b
C. El Shaddai: establish covenant, v 2
D. Abram falls on face, v 3a
E. God speaks: changes Abram’s name, vv 3b-8
F. Circumcision, vv 9-14
E’. God speaks: changes Sarai’s name, vv 15-16
D’. Abraham falls on face and laughs, v 17
C’. God: covenant with Isaac, promises to Ishmael, vv 18-21
B’. God ascended from Abe, v 22
A’. Abraham circumcises, is “99 years old”, vv 22-27
Many chiasms are even longer than this and contain a greater number of corresponding items.
If you map out the plot of Dumb and Dumber, you’ll find that the plot is structured as a chiasm, just like many passages of Hebrew scripture.
A: Lloyd pauses by side of the road, leers at a beautiful woman.
B: Mary rejects Lloyd.
C: Petey the parakeet dies.
D: A blind boy is scammed out of his money, then Harry and Lloyd spend the money.
E: Mental, the thug trying to kill Harry and Lloyd, is poisoned.
F: Lloyd pees in transit (empty beer bottles).
G: Exchange of vehicles: the Shaggin’ Wagon is traded in for a moped.
H: Harry begins walking back to Providence/ Harry and Lloyd get back together.
F’: Harry pees while in transit (becomes frozen to Lloyd).
G’: Exchange of vehicles: moped traded in for Lamborghini Diablo.
E’: Harry given laxatives.
D’: Mary/the kidnappers are scammed out of their money when Harry and Lloyd discover what’s in the briefcase.
C’: A spotted owl dies.
B’: Mary rejects Lloyd.
A’: Bus of beautiful women pauses by side of the road, women leer at Lloyd and Harry.
Pretty neat, eh?
And then there’s the matter of the coda of the film, which matches the center of the chiasm.
I’: Harry and Lloyd get back together after fighting/Harry and Lloyd begin walking back to Providence.