Blake explores four main areas of language secrecy. He argues, firstly, that secrecy is often evident when people use language to tease or amuse, an impulse that generates such linguistic activities and forms as word games, riddles, and even slang – a form of language that is often self-consciously inventive and challenging, and perversely oblique. Secondly, he argues that language is sometimes used obliquely and secretly out of a need for security, evident especially in the arcane world of codes and ciphers, but also in the secret worlds of pig Latin, back slang, and even rhyming slang. These secret worlds and the like partake of the essentially ludic intent of the realm of word games, riddles, and slang, but they involve secrets that, like the codes and ciphers, are meant to be understood only by an inner group. These secret worlds also render to the participants a sense of group solidarity, and this leads to the third function of secret language, its role in the maintenance of a sense of group identity. Subcultures often develop an argot, a form of language that is largely not understood by the mainstream culture, and this language serves to differentiate and bond the subculture, and to express its central interests and values. Fourthly, Blake argues that secrecy often becomes part of language from a deep-seated fear of the power of words, especially in cultures that overtly express a belief in the supernatural.

The book often focuses on the game-like qualities of language. The early section on word games examines the relatively straightforward playfulness of anagrams, acronyms, and acrostics. Blake takes us through more complex forms of wordplay. There is the palindrome, the word or phrase that reads the same in either direction (as level or rotator). I did not know that palindromes are also called sotadics, after the earliest examples from the third century bc Greek poet Sotades (who, apparently, was scurrilous as well as sodatic). And I had never heard of a semordnilap (the plural of palindrome reversed), where one word reveals another word when spelled backwards, as in paws/swap and diaper/repaid. Semordnilaps can be cross-cultural and cross-linguistic, as when Obama semordnilapses into Latin amabo ‘I will love’. Lipograms are texts where one particular letter is never used, and the univocalic text uses only one vowel.

After the discussion of word games, riddles, and other forms of wordplay, Blake moves on to the more serious and dangerous world of codes and ciphers, which have often been used in high-power politics and espionage. There is still a game-like, albeit mathematical, quality about ciphers and codes, but the purposes of these codes and ciphers are to establish a secret form of communication, and failure in this kind of game brings high costs. Blake relates how Mary Queen of Scots lost her head when the code used in messages to her supporters was decoded by one of the employees of Sir Francis Walsingham, Elizabeth’s chief spy. Even the successful breaking of a code in wartime does not necessarily bring joy to all on the code-breaking side. When the British broke a cipher revealing that the Germans were to shoot down an airliner supposedly carrying Winston Churchill, they did not want to reveal that they had broken the cipher, and the airliner had to be allowed to be shot down – with the unlucky actor Leslie Howard aboard, accompanied, unfortunately, by a companion of Churchillian appearance.

Words themselves often carry secret power, especially in societies that believe there is a significant (rather than an arbitrary) relationship between a word and what it refers to. The supernatural power of words is evident in many linguistic forms, from the magic formulas of the abracadabra and open sesame kind, to the incantations of the medieval world that often combine pagan and Christian elements, and to the power of names that is evident in traditions as disparate as Lohengrin and Turandot. In China in 1777, a lexicographer was executed for including the emperor’s name in a dictionary, in a way that breached the taboo against writing the emperor’s name. Taboo, indeed, is one of the main impulses for secret language, from the complex avoidance languages of many societies to the taboo on the name of a person after a death, a taboo that has led to one of the most recent borrowings from Aboriginal languages into Australian English – kumanjayi (with many variants), as a substitute name for a person who has recently died. Subcultures often develop detailed lexicons as protection against the oppression of the wider culture. Blake examines, for example, the argot of British thieves and beggars from the sixteenth century onwards, the Parlyaree of British itinerant entertainers, and the Polari of British gay culture.

The computer often appears in Blake’s narrative. It makes a surprising appearance in the discussion of Francis Bacon’s The Advancement of Learning, where there is a fascinating example of a cipher combined with steganography (another word that was new to me: ‘the practice of hiding a secret message inside another message’), which prefigures the binary notation of computers. The computer is evident in a number of references to the film 2001: A Space Odyssey (1968), which contains a computer with the name HAL. Blake describes early in the book how Julius Caesar used one of the earliest known ciphers in his private letters, a simple cipher that involved substituting the required letter with the one three places on in the alphabet. Blake supports the theory that HAL’s name is derived from a Caesar-type cipher of minus one from the name of the technology company IBM (although Arthur C. Clarke rejected this, pointing to the fact that the novel derives it from ‘Heuristically programmed ALgorithmic computer’). Cipher or acronym, the evil HAL serves as a useful focal point for the forms of secret language that lie at the heart of this book.

HAL is seemingly clever and powerful, but he is entirely programmed. In 1962 the Bell Laboratories used the song ‘Daisy, Daisy, Give Me Your Answer Do’ in their first experiments in speech synthesis, and this must have been one of the first ‘bits’ of information learned by HAL. When HAL malfunctions, the astronaut Dave Bowman proceeds to dismantle the computer’s cognitive functions, and the final step in its regression is a rendition of ‘Daisy’. The human capacity for language is the very opposite of this, even if Hal’s regression seems very much like a process of dementia. Blake’s finely argued and entertaining book demonstrates the extraordinary and un-machine-like nature of the inventiveness of human language – even when it seeks in multifarious forms of secrecy to hide its meanings from us.