Sign Languages
Sign languages are complete natural languages with their own grammars — how they arise, how they differ from spoken languages, and why they matter to linguistics.
Sign languages are natural human languages produced with the hands, face, and body. There are more than 300 of them worldwide, and they are unrelated to the spoken languages surrounding them: American Sign Language (ASL) is historically closer to French Sign Language than to British Sign Language, because a French educator, Laurent Clerc, brought his language to Connecticut in 1817. Deaf children invent sign languages from scratch when none is available, and the systems they invent show the seeds of grammar within one or two generations.
They are not pantomime
Linguists confirmed in the 1960s (William Stokoe's analysis of ASL) that sign languages have the same structural machinery as spoken ones: meaningless units (handshape, location, movement) combine into meaningful signs, which combine by grammatical rules into unbounded sentences. Sign languages have morphology (modulating a verb to mark who did what to whom), syntax with its own word order, regional accents, slang, and poetry. They are processed by the same left-hemisphere language networks as speech — phrase structure grammar is not an artifact of sound.
What they show about language
Because they emerged full-grown in isolated communities (Nicaragua's deaf schools produced a full sign language in the 1980s, grammaticalized within a decade as the first children grew up together), sign languages are the clearest evidence that language structure arises from human cognition rather than from vocal anatomy. The International Phonetic Alphabet had to be extended with symbols for handshape and movement to transcribe them; kinship and community structure explain how they spread.
Legal and educational status
Dozens of countries now recognize their sign languages legally; New Zealand Sign Language became an official language in 2006. The historical suppression of sign education — the Milan Congress of 1880 banned it from Deaf schools for a century — is a standing caution in language policy: a signed child deprived of fluent sign input does not emerge speaking better, but deprived of full language during the critical years.
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deaf culture language linguistics sign language