ASL is also used (sometimes alongside indigenous sign languages) in the Philippines, Malaysia, Singapore, Hong Kong, Dominican Republic, El Salvador, Haiti, Puerto Rico, Côte d'Ivoire, Burkina Faso, Ghana, Togo, Benin, Nigeria, Chad, Gabon, Democratic Republic of the Congo, Central African Republic, Mauritania, Kenya, Madagascar, and Zimbabwe. Like other sign languages, its grammar and syntax are distinct from any spoken language in its area of influence. While there has been no reliable survey of the number of people who use ASL as their primary language, estimates range from 500,000 to 2 million in the U.S. alone .
In the United States, as in most of the world, hearing families with deaf children often employ ad-hoc home sign for simple communications. Today though, ASL classes are offered in many secondary and postsecondary schools. ASL is a language distinct from spoken English—complete with its own syntax and grammar and supporting its own culture. The origin of modern ASL is ultimately tied to the confluence of many events and circumstances, including historical attempts at deaf education; the unique situation present on a small island in Massachusetts; the attempts of a father to enlist a local minister to help educate his deaf daughter; and in no small part the ingenuity and genius of people (in this case deaf people) for language itself.
Indigenous Peoples of the American Plains used Plains Indian Sign Language as an interlanguage for communication between people/tribes not sharing a common spoken language; its influence on ASL, if any, is unknown.
Off the coast of Massachusetts, on the island of Martha's Vineyard in the 18th century, the population had a much higher rate of deafness than the general population of the continental United States because of the founder effect and the island's isolation. Martha's Vineyard Sign Language was well known by almost all islanders since so many families had deaf members. It afforded almost everyone the opportunity to have frequent contact with a sign language while at an age most conducive to effortlessly learning a language.
Congregationalist minister and deaf educator Thomas Hopkins Gallaudet is credited with popularizing the signing technique in North America. At the behest of a father who was interested in education for his deaf daughter, Alice Cogswell, Gallaudet was enlisted to investigate methods of teaching the deaf. In the early 1800s he visited the Abbé de l'Épée's school in Paris and convinced one of the teachers, Laurent Clerc, to return with him to America. In 1817 they founded the American Asylum for the Deaf and Dumb (now the American School for the Deaf), in Hartford, Connecticut, to teach sign language to American deaf students.
It was at this school that all these influences would intermingle, interact and what would become ASL was born. Many of the school's students were from Martha's Vineyard, and they mixed their "native" sign language with Clerc's OFSL. Other students probably brought their own highly localized sign language or "home sign" systems to the mix. Undoubtedly, spontaneous lexicon developed at the school as well. If there was any influence from sign language of indigenous people, it may have been here that it was absorbed into the language.
Interestingly, because of the early influence of the sign language of France upon the school, the vocabularies of ASL and modern French Sign Language are approximately 60% shared, whereas ASL and British Sign Language, for example, are almost completely dissimilar.
From its synthesis at this first public school for the deaf in North America, the language went on to grow. Many of the graduates of this school went on to found schools of their own in many other states, thus spreading the methods of Gallaudet and Clerc and serving to expand and standardize the language; as with most languages though, there are regional variations.
ASL is a natural language as proved to the satisfaction of the linguistic community by William Stokoe, and contains phonology, morphology, semantics, syntax and pragmatics just like spoken languages. It is a manual language or visual language, meaning that the information is expressed not with combinations of sounds but with combinations of handshapes, palm orientations, movements of the hands, arms and body, location in relation to the body, and facial expressions. While spoken languages are produced by the vocal cords only, and can thus be easily written in linear patterns, ASL uses the hands, head and body, with constantly changing movements and orientations. Like other natural sign languages, it is "three dimensional" in this sense. ASL is used natively and predominantly by the Deaf and hard-of-hearing of the United States and Canada.
However, Edward Klima and Ursula Bellugi have modified the common theory that signs can be self-explanatory by grouping signs into three categories:
Klima and Bellugi used American Sign Language in formulating that classification. The theory that signs are self-explanatory can be conclusively disproved by the fact that non-signers cannot understand fluent, continuous sign language. The majority of signs are opaque.
Generally, signs that are "Transparent" are signs of objects or words that became popular after the basics of ASL were established. There are, of course, exceptions to this.
ASL includes both fingerspelling borrowings from English, as well as the incorporation of alphabetic letters from English words into ASL signs to distinguish related meanings of what would otherwise be covered by a single sign in ASL. For example, two hands trace a circle to mean 'a group of people'. Several kinds of groups can be specified by handshape: When made with C hands, the sign means 'class'; when made with F hands, it means 'family'. Such signs are often referred to as initialized signs because they substitute the first initial an English word as the handshape in order to provide a more specific meaning.
When using alphabetic letters in these ways, several otherwise non-phonemic handshapes become distinctive. For example, outside fingerspelling there is but a single fist handshape, with the placement of the thumb irrelevant, but within fingerspelling the position of the thumb on the fist distinguishes the letters A, S, and T. Letter-incorporated signs which rely on such minor distinctions tend not to be stable in the long run, but they may eventually create new distinctions in the language. For example, due to signs such as 'elevator', which generally requires the E handshape, some argue that E has become phonemically distinct from the 5/claw handshape.
Fingerspelling has also given way to a class of signs known as "loan signs" or "borrowed signs." Sometimes defined as lexicalized fingerspelling, loan signs are somewhat frequent and represent an English word which has, over time, developed a unique movement and shape. Sometimes loan signs are not even recognized as such because they are so frequently used and their movement has become so specialized. Loan signs are sometimes used for emphasis (like the loan sign #YES substituted for the sign YES), but sometimes represent the only form of the sign (e.g., #NO). Probably the most commonly used example of a loan sign is the sign for NO. In this sign, the first two fingers are fused, held out straight, and then tapped against the thumb in a repeated motion. When broken down, it can be seen that this movement is an abbreviated way of fingerspelling N-O-N-O. Loan signs are usually glossed as the English word in all capital letters preceded by the pound sign(#).Other commonly known loan signs include #CAR, #JOB, #BACK, #YES, and #EARLY.
There are two true writing systems in use for ASL: a phonemic Stokoe notation, which has a separate symbol or diacritic mark for every phonemic hand shape, motion, and position (though it leaves something to be desired in the representation of facial expression), and a more popular iconic system called SignWriting, which represents each sign with a rather abstract illustration of its salient features. SignWriting is commonly used for student newsletters and similar purposes.
Many parents use a collection of simplified or ad hoc signs called "baby sign", as infants do not have the dexterity required for true ASL. However, parents can learn to recognize their baby's approximations of adult ASL signs, just as they will later learn to recognize their approximations of oral language, so teaching an infant ASL is also possible. Typically young children will make an ASL sign in the correct location and use the correct hand motion, but may be able only to approximate the hand shape, for example, using one finger instead of three in signing water.