Constrained writing is a catch-all literary term for a whole host of written forms or techniques that limit what or how authors or poets write by forcing them to use a specific set of words, or to work within a strict set of rules or parameters. In simple terms, poetry and even song-writing can be considered examples of constrained writing, since their lines often need to rhyme or contain a fixed number of syllables or beats. Some forms of poetry are naturally more rigid then others—haikus, for instance, fit their 17 syllables into the strict pattern 5–7–5, while all but three of William Shakespeare’s 154 sonnets follow the rhyme scheme ABAB–CDCD–EFEF–GG—but at the most extreme, some forms of constrained writing are even more self-limiting and end up being very, very constrained indeed.

1. MANDATED VOCABULARY

One of the simplest forms of constrained writing is limited or mandated vocabulary, wherein a writer either prohibits certain words or else limits themselves to a particular set or number of words, or to words that fit a particular brief. Doug Nufer’s appropriately-titled 2004 novel Never Again, for instance, didn’t use a single word more than once. Le Train de Nulle Part (The Train From Nowhere) by the French novelist Michel Thaler didn’t contain a single verb. And the 2008 novel let me tell you by Paul Griffiths comprised only the 483 words spoken by Ophelia in Shakespeare’s Hamlet.

But probably the most famous example of a work of mandated vocabulary is Dr. Seuss’s Green Eggs And Ham (1960), which was written in response to a bet between Seuss and his publisher, Bennett Cerf, that he could not complete a story using no more than 50 different words. Seuss returned with a work using only the words a, am, and, anywhere, are, be, boat, box, car, could, dark, do, eat, eggs, fox, goat, good, green, ham, here, house, I, if, in, let, like, may, me, mouse, not, on, or, rain, Sam, say, see, so, thank, that, the, them, there, they, train, tree, try, will, with, would and you, and won the bet.

2. LIPOGRAM

A lipogram is a literary work in which a particular letter of the alphabet is intentionally avoided. The difficulty of writing lipograms obviously depends on the frequency of the letter or letters in question (after all, this description entirely avoids using the letter Z without a problem), but things get really tough when it’s the most common letters in the language that are excluded.

None of the more than 50,000 words in Ernest Vincent Wright’s novel Gadsby contain the letter E, for instance, and nor do any of the words in the French writer Georges Perec’s 1969 novel La Disparition—which was translated into English, still following Perec’s original rule, by the writer and critic Gilbert Adair in 1995 and published under the title A Void. Perec later published a novella, Les Revenentes (1972), incidentally, in which E was the only vowel.

3. RHOPALISM

A rhopalic poem or sentence is one in which each successive word is one letter (or, typically in poetry, one syllable) longer than the previous one. Due to the fact that the personal pronoun, I, is only one letter long in English, shorter sentences that follow this rule are fairly easy to construct (“I am now here,” “I do her hair,” “I go and walk there weekly”) but as the sentences get longer, rhopalism becomes an increasingly tough rule to follow. In 1965, however, the linguist and author Dmitri Borgmann came up with a staggering 20-word sentence that followed the rules of rhopalism perfectly:

“I do not know where family doctors acquired illegibly perplexing handwriting; nevertheless, extraordinary pharmaceutical intellectuality, counterbalancing indecipherability, transcendentalizes intercommunications’ incomprehensibleness.”

4. ABECEDARIUS

An abecedarius is a specific type of acrostic poem in which successive lines or verses begin with each letter of the alphabet in order. Geoffrey Chaucer’s 23-verse poem "A. B. C."—written in the 14th century, before J, U and W were even added to the English alphabet—is among the form’s most famous examples.

5. PALINDROME

A palindrome is of course a word (civic, radar, rotator) or a phrase (“don’t nod,” “was it a cat I saw?”) that reads the same backwards as forwards. As a form of constrained writing, however, palindromes can be extended to extraordinary lengths: In his 2012 book, This Is A Book, the comedian and writer Demetri Martin compiled a 500-word poem “about a guy in a strip club who becomes infatuated with two strippers, Tina and Stella.” The entire poem—which opens “Sexes. / Eh, the sexes. / Never even. Still, it’s DNA.”—reads the same backwards and forwards.

6. TAUTOGRAM

A tautogram is an extreme form of alliteration in which all of the words in a sentence or phrase begin with the same letter. Just like a palindrome, it’s a form of constrained writing that can be taken to extraordinary extremes—as in the 1974 novel Alphabetical Africa, by the Austrian-born American novelist Walter Abish.

Chapter 1 of the book contains only words beginning with A. In chapter 2, words beginning with B are introduced alongside the A-words, followed by C-words in chapter 3, and so on, until chapter 26 is entirely unrestrained. The remaining 26 chapters of the book then proceed to restrict the writing, first by removing the Z-words in chapter 27, then the Y-words in chapter 28, and so on until chapter 52, which is again limited only to words beginning with A.

7. PANGRAM

A pangram is a sentence that contains every letter of the alphabet. The most famous example is “the quick brown fox jumps over the lazy dog” (which is believed to have originally been introduced in the 1880s as a handwriting exercise, before being picked up by typists and stenographers), while less familiar pangrams include “the five boxing wizards jump quickly” and “jackdaws love my big sphinx of quartz.”

“The quick brown fox” runs to a total of 35 letters, although it can be reduced to 33 by replacing the first “the” with “a.” But the aim of pangram writing is obviously to produce as short a sentence as possible, with the ultimate goal being a perfectly grammatical sentence containing just 26 letters. Understandably so-called “perfect” pangrams like these often end up incorporating abbreviations, obscure words, and alternative spellings, but a handful of examples have nevertheless been created, including “Mr. Jock, TV quiz Ph.D., bags few lynx” and “cwm fjord-bank glyphs vext quiz” (a cwm being a Welsh valley, and vext being an old spelling of vexed).

8. PILISH

Pilish is an extraordinary form of constrained writing that straddles the boundary between language and mathematics: Pilish literature is written in such a way that the number of letters in each successive word is equal to the successive decimal places of pi, 3.14159265359…

The first few numbers of pi can be memorized using the mnemonic “How I wish I could calculate pi,” while extra decimal places can be added by memorizing ever longer sentences (“How I want a drink, alcoholic of course, after the heavy lectures involving quantum mechanics” takes pi to its 14th decimal place). But as a form of constrained writing, Pilish was taken to an extreme by the American mathematician Mike Keith in his 1996 short story Cadaeic Cadenza, which comprises 3835 words all following the decimal sequence of pi (0s are words 10 letters long). As if that weren’t mindboggling enough, in 2010 Keith published the novella Not A Wake—which pushed that total to 10,000.