Trilogy

A trilogy is a set of three works of art that develop a single theme. Trilogies are commonly found in literature and occasionally in film (for example, Back to the Future). Some authors of popular trilogies may later extend the series by adding more works to it, thus technically making the series no longer a trilogy. This happened in the case of Isaac Asimov's Foundation series, which was originally three books, and also in The Hitch Hikers Guide to the Galaxy, a series of five novels which the author Douglas Adams, for humorous effect, continued to dub a "trilogy" by his own fiat for the rest of his life).

Other famous trilogies include:

• USA, three novels by John dos Passos
• The Gormenghast trilogy by Mervyn Peake
• Peter Jackson's The Lord of the Rings movies

But not:

• The Lord of the Rings book/books

Although initially published in three volumes, The Lord of the Rings (LOTR) is actually a single work rather than a trilogy. Ironically, in the 1960s when it burst into worldwide popularity fans dubbed it "the trilogy" (or even the trilogy). Tolkien himself, however, divided the novel into six books plus five appendices in keeping with the literary device wherein Tolkien pretends to have "discovered" Middle-earth and to be describing it as befits a scholar of linguistics and ancient history. In the late 1990s, LOTR became available in both one-volume and seven-volume editions (in addition to several three-volume editions).