Sign languages are natural languages expressed primarily through movements and configurations of the hands, face, and body rather than through speech. They have conventional vocabularies and grammatical systems capable of conveying abstract ideas, emotions, and complex information. Many developed within Deaf communities, although hearing people also use them. “Sign language” denotes a category of languages, not a single worldwide system: different communities use distinct languages that are not necessarily mutually intelligible. Sign languages are neither simplified substitutes for speech nor merely collections of gestures. (bda.org.uk)
Diversity and relationships
American Sign Language (ASL), British Sign Language (BSL), and French Sign Language (LSF) are separate languages. Their relationships do not simply follow those of surrounding spoken languages. ASL and BSL differ substantially despite the widespread use of English in their respective communities. ASL developed through contact between local signing traditions and LSF; modern ASL and LSF nevertheless remain distinct. A shared spoken language therefore does not establish a shared signed language. (nidcd.nih.gov)
Variation also exists within individual sign languages. Regional dialects, differences between generations, and individual styles can affect vocabulary, movement, rhythm, and expression. These patterns belong to the study of sociolinguistics, just as comparable variation does in spoken languages. National labels are useful identifiers but should not be mistaken for descriptions of completely uniform usage. (nidcd.nih.gov)
International Sign is a cross-language communication practice used at international gatherings and in other encounters between signers without a common language. It draws on shared conventions and context-dependent resources rather than constituting a universal language known by all deaf people. Some settings have developed relatively extensive conventional vocabularies, but familiarity with International Sign varies among users. (wfdeaf.org)
Linguistic structure
Sign-language linguistics examines the same broad organizational levels found in spoken languages, including phonology, morphology, syntax, and semantics. Here, phonology concerns the organization of contrastive form rather than necessarily sound. Descriptions of signs distinguish features such as handshape, location, and movement. A sign can consequently be analyzed into components rather than treated as an indivisible picture or gesture. William Stokoe’s research and the dictionary produced with Dorothy Casterline and Carl Croneberg helped establish this approach. (gupress.gallaudet.edu)
The face and body are integral to linguistic expression. Nonmanual features, including eyebrow movements, mouth patterns, head movements, and posture, contribute to meaning alongside the hands. They are not simply emotional embellishments. For example, ASL can use eyebrow and body movements to distinguish questions from statements. Because these features interact with manual signing, an account restricted to hand movements omits important information. (bda.org.uk)
Grammar is language-specific. BSL is not English represented with hand movements, and interpreting between the two requires attention to their different structures. Signed languages can also have rich inflectional morphology. Their linguistic organization therefore cannot be inferred merely by replacing spoken words with dictionary signs in the same order. (bda.org.uk)
Fingerspelling and related systems
Fingerspelling represents letters through conventional hand configurations. In ASL, it is used particularly for proper names and for identifying English words. It is part of the language’s repertoire, not the basis of all signed communication. Fingerspelling creates a connection with an alphabet and written vocabulary, while ordinary signs have their own linguistic forms. (nidcd.nih.gov)
Natural sign languages should be distinguished from constructed systems that combine signs with the grammatical organization of a spoken language. Such systems may borrow signs from BSL or another language without thereby becoming that language. The distinction concerns linguistic structure and community use, not simply whether the hands are involved in communication. (bda.org.uk)
History and community transmission
Sign languages develop through communication among their users rather than being the inventions of a single educator or committee. In the case of ASL, historical contact between signing communities contributed to its development. Academic recognition came much later than the language itself. In 1960, William Stokoe published structural research challenging the assumption that signing lacked linguistic organization; the 1965 dictionary further supported systematic study of ASL. (nidcd.nih.gov)
Sign languages are closely connected with Deaf culture and community institutions. They support social interaction as well as literature and other expressive traditions. Research publications document the languages, histories, cultures, and literary practices of signing communities, treating them as subjects of linguistic and cultural scholarship. (gupress.gallaudet.edu)
Language acquisition depends on access to language users. Children exposed to ASL through signing parents can acquire it naturally, while deaf children with nonsigning parents may encounter it through peers or other community members. Consequently, transmission need not follow only the parent-to-child pattern commonly assumed for spoken languages. (nidcd.nih.gov)
Accessibility and legal recognition
Sign-language interpreting enables communication between users of different languages. Interpreters convey meaning across linguistic structures rather than mechanically substituting individual words. Some settings also employ Deaf relay interpreters to communicate signed information to people requiring additional forms of access. (bda.org.uk)
Tactile signing allows signed communication to be received through touch. A recipient may rest their hands lightly on the signer’s hands to perceive movements. This provides a tactile channel for people who cannot fully access visual signing. (nationaldb.org)
The Convention on the Rights of Persons with Disabilities explicitly includes signed languages in its definition of language. Article 21 addresses their use in official interactions and their recognition and promotion. Article 24 addresses sign-language learning, Deaf linguistic identity, and education, while Article 30 recognizes sign languages and Deaf culture within cultural and linguistic identity. These provisions place signed communication within the international framework of human rights. (un.org)