Juan Pablo Bonet, Reducción de las letras y arte para enseñar a hablar a los mudos
("Reduction of letters and art for teaching mute people to speak") (Madrid, 1620)
Groups of deaf people have used sign languages throughout history. One of the earliest written records of a sign language is from the fifth century BC, in Plato's Cratylus, where Socrates says: "If we hadn't a voice or a tongue, and wanted to express things to one another, wouldn't we try to make signs by moving our hands, head, and the rest of our body, just as dumb people do at present?"
Until the 19th century, most of what is known about historical sign languages is limited to the manual alphabets (fingerspelling systems) that were invented to facilitate transfer of words from a spoken language to a sign language, rather than documentation of the language itself. Pedro Ponce de León (1520–1584) is said to have developed the first manual alphabet.
In 1620, Juan Pablo Bonet published Reducción de las letras y arte para enseñar a hablar a los mudos (‘Reduction of letters and art for teaching mute people to speak’) in Madrid. It is considered the first modern treatise of sign language phonetics, setting out a method of oral education for deaf people and a manual alphabet.
Chirogram from Chirologia
In Britain, manual alphabets were also in use for a number of purposes, such as secret communication, public speaking, or communication by deaf people. In 1648, John Bulwer described "Master Babington", a deaf man proficient in the use of a manual alphabet, "contryved on the joynts of his fingers", whose wife could converse with him easily, even in the dark through the use of tactile signing.
In 1680, George Dalgarno published Didascalocophus, or, The deaf and dumb mans tutor, in which he presented his own method of deaf education, including an "arthrological" alphabet, where letters are indicated by pointing to different joints of the fingers and palm of the left hand. Arthrological systems had been in use by hearing people for some time; some have speculated that they can be traced to early Ogham manual alphabets.
The vowels of this alphabet have survived in the contemporary alphabets used in British Sign Language, Auslan and New Zealand Sign Language. The earliest known printed pictures of consonants of the modern two-handed alphabet appeared in 1698 with Digiti Lingua (Latin for Language [or Tongue] of the Finger), a pamphlet by an anonymous author who was himself unable to speak. He suggested that the manual alphabet could also be used by mutes, for silence and secrecy, or purely for entertainment. Nine of its letters can be traced to earlier alphabets, and 17 letters of the modern two-handed alphabet can be found among the two sets of 26 handshapes depicted.
Charles de La Fin published a book in 1692 describing an alphabetic system where pointing to a body part represented the first letter of the part (e.g. Brow=B), and vowels were located on the fingertips as with the other British systems. He described such codes for both English and Latin.
By 1720, the British manual alphabet had found more or less its present form. Descendants of this alphabet have been used by deaf communities (or at least in classrooms) in former British colonies India, Australia, New Zealand, Uganda and South Africa, as well as the republics and provinces of the former Yugoslavia, Grand Cayman Island in the Caribbean, Indonesia, Norway, Germany and the United States.
Frenchman Charles-Michel de l'Épée published his manual alphabet in the 18th century, which has survived basically unchanged in France and North America until the present time. In 1755, Abbé de l'Épée founded the first school for deaf children in Paris; Laurent Clerc was arguably its most famous graduate. Clerc went to the United States with Thomas Hopkins Gallaudet to found the American School for the Deaf in Hartford, Connecticut, in 1817. Gallaudet's son, Edward Miner Gallaudet, founded a school for the deaf in 1857 in Washington, D.C., which in 1864 became the National Deaf-Mute College. Now called Gallaudet University, it is still the only liberal arts university for deaf people in the world.
Sign languages generally do not have any linguistic relation to the spoken languages of the lands in which they arise. The correlation between sign and spoken languages is complex and varies depending on the country more than the spoken language. For example, the US, Canada, UK, Australia and New Zealand all have English as their dominant language, but American Sign Language (ASL), used in the US and English-speaking Canada, is derived from French Sign Language whereas the other three countries sign dialects of British, Australian and New Zealand Sign Language. Similarly, the sign languages of Spain and Mexico are very different, despite Spanish being the national language in each country, and the sign language used in Bolivia is based on ASL rather than any sign language that is used in a Spanish-speaking country. Variations also arise within a 'national' sign language which don't necessarily correspond to dialect differences in the national spoken language; rather, they can usually be correlated to the geographic location of residential schools for the deaf.
International Sign, formerly known as Gestuno, is used mainly at international deaf events such as the Deaflympics and meetings of the World Federation of the Deaf. While recent studies claim that International Sign is a kind of a pidgin, they conclude that it is more complex than a typical pidgin and indeed is more like a full sign language.