Gödel, Escher, Bach: An Eternal Golden Braid by Douglas Hofstadter is an intricate and complex study of Strange Loops, Meta-Concepts in general and their connection to self-awareness and intelligence. Each chapter is separated from the next by a short fictional piece in the style of Lewis Carroll, which exemplifies the theme of the following chapter. The drawings of M. C. Escher and the Surrealist paintings of René Magritte are used as illustrations.
Mathematical, logical and computer-science concepts discussed in this book include:
- Gödel's incompleteness theorem
- The Epimenides paradox
- Zeno's paradoxes
- Euclid's Theorem
- Non-Euclidean geometry
- Propositional Calculus
- Fermat's Last Theorem
- The Church-Turing Thesis
- Cantor's diagonal method
- Goldbach's conjecture
The Dialogues contain examples of:
- All Just a Dream: The Subjunc-TV dialogue is All Just A Hypothetical Situation.
- All There in the Index: For example, to find where the true end of Aria with Diverse Variations is, search for 'typos'.
- Arc Words: "RICERCAR".
- Artificial Intelligence: Discussed.
- Breather Episode: The interlude "English French German Suite", consisting of Lewis Carroll's poem "Jabberwocky" in three languages, taking place between two chapters of theories on how the human mind works.
- Cultural Translation: Several have been approved by the author.
- Foreshadowing: Looking at the semantic network on page 370 reveals a lot about the latter half of the book.
- Fun with Acronyms:
- The chapter "Contracrostipunctus", which contains an acrostic which itself contains an acrostic.
- RICERCAR and CEGABBAB ("Babbage, C(harles)" backwards) show up in the last chapter.
- GoldSilverCopper Standard: ... Well, okay, not really. But the words "Copper", "silver", and "gold" appear (in that order) in several places.
- Gratuitous Foreign Language: French and Latin are frequently used in this manner.
- Harassing Phone Call: Achilles begins the dialogue "Air on G's String" by telling the Tortoise about an obscene phone call he received in which the caller merely shouted twice before hanging up, "Yields falsehood when preceded by its quotation!" When the Tortoise teaches him about quines, he realizes that the caller was stating a logical paradox.
- Here We Go Again!: The ending, which also makes the entire book into a Framing Device for itself.
- Hidden in Plain Sight: The answers to the puzzles in "Sonata for An Unaccompanied Achilles." Not only is the answer explicitly used in the text, it is also the two puzzles make up the entire word.
- In Name Only: By the author's own admission (in the Overview), the dialogue "Chromatic Fantasy, And Feud" bears "hardly any resemblance, except in title, to Bach's Chromatic Fantasy and Fugue."
- Koan: On a whole bunch of baffling ones.
- Logic Bomb: The book shows how Gödel's Incompleteness Theorem does this to mathematics.
- Metafiction: Some stories are so extremely meta that they have no content other than discussions of themselves discussing themselves discussing themselves ad infinitum, usually indirectly.
- Musical Theme Naming: Every dialogue is named after a piece by Johann Sebastian Bach, or a pun on one.
- Nested Story: "Little Harmonic Labyrinth", which actually ends while still one level "down".
- Newhart Phonecall: the "Sonata for An Unaccompanied Achilles".
- Our Genies Are Different:
- In the dialogue "Little Harmonic Labyrinth," Genies are allowed to grant wishes, but not wishes about wishes, which are known as meta-wishes. Meta-Genies (who come from Meta-Lamps) are allowed to grant meta-wishes, but not wishes about meta-wishes, which are within the authority of Meta-Meta-Genies. The word "Djinn" is generically used to designate Genies, Meta-Genies, Meta-Meta-Genies, and all others in GOD (which stands for "GOD Over Djinn").
- In the chapter "Typographical Number Theory," "djinn" is an undefined term used in place of "natural number" in setting out the five Peano postulates, with "genie" taking the place of zero.
- Public Domain Character: Achilles and the Tortoise, from the Greek philosopher Zeno (who also himself appears).
- Punny Name: The coppers Silva and Gould, as well as the ant collective Aunt Hillary.
- Recursive Acronym: "GOD" in "Little Harmonic Labyrinth" (short for "GOD Over Djinn").
- Recursive Reality. In so many ways.
- Running Gag: This dialogue, repeated, at least, some variation of, thrice; on pages 62, 200, and 724.Achilles: Say, don't you play the guitar?
Tortoise: Fiddle. It makes a big difference, you know.
Achilles: Oh, well, it's all the same to me.
- Schrödinger's Butterfly: The book uses several of these, nesting several layers of drama. In the dialogue "Little Harmonic Labyrinth," Achilles and the Tortoise are on an airship and start reading a book about themselves. The bad news is that the story doesn't "pop back" all the way to the last level, and the initial story is still left hanging. The good news is that the Tortoise and Achilles can move up to a previous level using popcorn.
- She's a Man in Japan: The Tortoise is referred to as male in the original, but the French word for tortoise is the feminine tortue. Hofstadter, who is interested in the phenomenon of unconscious sexism in language, was delighted when this was pointed out, and gave the French translators the go-ahead to make the Tortoise a female character.
- Self-Deprecation: A book about "metal-logic", called Copper, Silver, Gold: an Indestructible Metallic Alloy is mentioned in the dialogues. The Crab says that it's "filled with strange Dialogues about many subjects, including molecular biology, fugues, Zen Buddhism, and heaven knows what else." Achilles responds that "probably some crackpot wrote it". The book is also listed in the bibliography, where it's called "a formidable hodge-podge, turgid and confused". Indeed very little praise is given to its author, Egbert B. Gebstadter.
- Self-Fulfilling Prophecy: Commented on if a psychic who could determine the minds of other people was allowed to choose his or her jury if accused.
- Sick Episode: "Sonata for Unaccompanied Achilles," a dialogue for one in which Achilles is telephoned by the Tortoise, who is apparently suffering from a headache. (The readers only get Achilles' side of the conversation.)
- Significant Anagram: Terry Winograd, author of SHRDLU, becomes "Dr. Tony Earrwig" in the dialogue "SHRDLU, Toy of Man's Designing."
- Spoiled by the Format: The Tortoise and Achilles discuss using Filler to counteract this problem.
- Subverted Rhyme Every Occasion: In one of the dialogues, the Crab puts on a record of himself singing "A Song Without Time or Season." Here's how it goes:A turner of phrases quite pleasin',
Had a penchant for trick'ry and teasin'.
In his songs, the last line
Might seem sans design;
What I mean is, without why or wherefore.
- This is lampshaded almost immediately:Achilles: Lovely! Only I'm puzzled by one thing. It seems to me that in your song, the last line is—
Crab: Sans design?
Achilles: No ... What I mean is, without rhyme or reason.
- This is lampshaded almost immediately:
- Textbook Humor: Well, the text wasn't all that serious to begin with, but you have to wonder when Hofstadter describes the DNA of a feline as CATCATCATCATCAT...
- Title Drop: In the form of Bookends.
- To Be Continued: The two Dialogues Prelude... and ... Ant Fugue are, well, two sections of a separated story. The end of the former ends with TTortoise [sic], while the latter begins with Achilles and CCrab [sic], using "ATTACCA" note as a guide.
- The Treachery of Images: Subverted—one character takes the pipe out of the Magritte painting and smokes it.
- Turing Test: Parodied in the final chapter, where Alan Turing and Charles Babbage each try to prove that the other is a computer invented by them. Turing insists on calling it a "Babbage test."
- Viewers Are Geniuses: The dialogues, especially, conceal mathematical jokes that aren't explained in the text. For example, in a spoof of Fermat's Last Theorem, the Tortoise claims to have found a counterexample in which the exponent n is "the only positive integer which does not occur anywhere in the continued fraction for pi". Mathematically inclined readers will know that, while the famous constants e and sqrt(2) have highly patterned continued fractions, that for pi is quasi-random, so the Tortoise's claim is of no help at all in finding the value of n.
- Your Princess Is in Another Castle!: A unique version of a fake ending which takes place after the actual ending.