No, five parts. Hitchhikes's Guide - Restaurant at the End of the Universe - Life, The Universe, and Everything - So Long, And Thanks for all the Fish - and finally, Mostly Harmless.
comment #43534 I don't know if you were joking so I'll just explain. Before the third Scary Movie, "The Best Trilogies Come in three's" joke was about the new Star Wars films.
"the best trilogies come in 3's" "No, the Hitchhiker's Guide to the Galaxy is a trilogy in four parts."
a trilogy is, BY DEFINITION, a series in three parts. the word's root "tri" means THREE, you know. so there's no such as a 4-part, 5-part, 6-part, etc trilogy. a 4-part series would be a TETRALOGY 5, PENTAlogy 6, HEXAlogy etc
The fact that mLegion brought up about ALL trilogies being 3-part is not just correct because of a coincidental fact, but because there's no way it could be otherwise.
Actually, I don't think it was. You'd be surprised how many people don't know that trilogy = 3 parts. Hence the existence of jokes like "the best trilogies come in threes" and "a trilogy in four parts"... It's ironic stupidity, which like all ironic stupidity parodies/mocks those people whom suffer from genuine stupidity (a la Borat, Ali G and other such "mockumentary" stuff).