Sign languages are languages, and each one is its own

The misconceptions about sign languages are consistent and worth clearing before anything else.

They are not universal. Different countries have different sign languages, and languages used in countries with the same spoken language are frequently unrelated — British and American sign languages, for instance, are not mutually intelligible, while American and French sign languages are historically related.

They are not manual encodings of spoken languages. They have their own grammar, their own vocabulary and their own syntax, none of which follows the surrounding spoken language.

They are not simplified. Linguistic research over the past several decades has established that sign languages have the full structural complexity of spoken languages, including phonology, morphology and syntax.

The phonology of a language without sound

Sign languages have a level of structure equivalent to phonology, where meaningless units combine to form meaningful ones.

The parameters are handshape, location, movement, orientation and non-manual features. Changing one parameter can change a sign into a different sign, exactly as changing one sound changes a spoken word.

Each sign language has its own inventory of permitted handshapes and its own constraints on how they combine, which differ between languages just as sound inventories do.

What the visual modality allows

This is where sign languages do things spoken languages cannot do easily.

Use of space. Signers establish reference points in the space in front of them, and then refer back to them by directing signs toward those locations. This produces a grammatical system for tracking who is doing what to whom that has no direct spoken equivalent.

Directional verbs. Many verbs move between established locations to indicate subject and object, incorporating agreement into the movement itself.

Simultaneity. Because two hands, the face and the body are available at once, several pieces of information can be expressed simultaneously rather than in sequence. Spoken languages are largely constrained to a linear stream.

Non-manual grammar. Facial expression and head position carry grammatical rather than emotional information — marking questions, conditionals, negation and topics. A raised eyebrow can be the equivalent of a question particle, and omitting it makes the sentence ungrammatical.

Classifier constructions, where handshapes representing categories of object move through space to describe spatial relationships and motion with a precision that spoken description struggles to match.

How they arise

Sign languages emerge wherever deaf people form communities.

Some developed in and around schools for deaf children, which brought together a population that had previously been dispersed. Several national sign languages trace to specific institutions.

Others arose in communities with a high incidence of inherited deafness, where hearing and deaf people alike signed — village sign languages, documented in several places, with the notable feature that deafness in such communities was not particularly isolating.

And there are cases where linguists have observed a sign language emerging in real time as a new deaf community formed, which is close to unique as an opportunity to watch a language come into existence. The documented sequence — from initial variable systems to a full grammar within a few generations — has been influential in debates about how language develops.

Home sign

Deaf individuals without access to a sign language community frequently develop gestural systems with their families, sometimes with considerable structure.

These are not full languages, and their existence is a reminder of what the isolated situation looks like, which is the condition many deaf people historically were in.

The history is not comfortable

For a long period, education policy in many countries actively suppressed sign languages in favour of oral methods, on the theory that signing impeded speech acquisition.

Children were prevented from signing, sometimes physically. The policy dominated deaf education for the best part of a century in many places, and its effects on educational outcomes and on language deprivation are documented and severe.

The shift back toward sign-based and bilingual education came from research and from Deaf-community advocacy, and it is far from complete. Access to a sign language in early childhood remains the crucial variable, since language deprivation in the critical period has lasting cognitive and social consequences.

Deaf culture

Many Deaf people understand themselves as members of a linguistic and cultural minority rather than as having a medical condition — a position frequently marked in English by capitalising Deaf when referring to cultural identity.

From that perspective, sign languages are the languages of communities with their own literature, humour, poetry, theatre and history, and technologies or policies aimed at eliminating deafness raise the same questions as any policy aimed at eliminating a language.

That framing is not universally held among deaf people, and the debate within and around these communities is real and ongoing. What is not in dispute among linguists is the status of the languages themselves.