BSL (British Sign Language) and ASL (American Sign Language) are two completely separate languages. Despite the fact that the UK and the US share English as a spoken language, their sign languages are not mutually intelligible. A deaf person fluent in ASL would not be able to follow a conversation in BSL, and vice versa. The reason comes down to history: the two languages evolved from entirely different roots.
Why British and American Sign Languages Are Unrelated
ASL traces its origins back more than 200 years to a blend of local American sign languages and French Sign Language (LSF). Laurent Clerc, a deaf educator from France, brought LSF to the United States in 1817 when he co-founded the first permanent school for the deaf in Hartford, Connecticut. That French influence shaped ASL’s vocabulary and grammar in ways that persist today.
BSL, on the other hand, developed independently within the UK’s deaf communities and schools, with no significant French influence. So ASL actually has more in common with French Sign Language than it does with BSL. The two languages belong to entirely different language families.
BSL’s Language Family
BSL didn’t stay confined to Britain. During the 19th century, deaf immigrants and educators carried it to Australia and New Zealand, where it evolved into Australian Sign Language (Auslan) and New Zealand Sign Language (NZSL). These three languages are so closely related that linguists group them under the acronym BANZSL. A 1987 study comparing core vocabulary found a 90% similarity between Auslan and BSL, leading researchers to suggest they could be considered dialects of the same language. NZSL and Auslan share between 87% and 96% of their vocabulary depending on how regional variants are counted.
ASL, meanwhile, sits in the French Sign Language family alongside the sign languages of several other countries that were influenced by French deaf education. Irish Sign Language is an interesting case: it shows influence from both French Sign Language (introduced by French nuns who established Catholic schools for deaf children) and BSL, placing it somewhere between the two families.
The Alphabet: One Hand vs. Two
The most immediately visible difference between ASL and BSL is how they fingerspell. ASL uses a one-handed manual alphabet. Every letter is formed with a single hand using distinct shapes, and you can spell an entire word without moving your other hand at all.
BSL uses a two-handed system. Your non-dominant hand serves as a base, with its fingers representing the vowels. Your dominant hand then points to or interacts with the non-dominant hand to form each letter. This looks completely different in practice, and it’s one of the first things people notice when comparing the two languages side by side. If you’ve learned to fingerspell in one system, you essentially have to start from scratch with the other.
Vocabulary Differences
Beyond the alphabet, the core vocabulary of BSL and ASL is largely different. One computational study comparing nearly 2,000 ASL signs and nearly 1,500 BSL signs found that only about 590 overlapped in meaning, and sharing a meaning doesn’t mean the signs look the same. The signs for common words like “thank you,” “help,” or “family” are performed with entirely different hand shapes, movements, and positions in each language.
There are occasional similarities, sometimes by coincidence and sometimes because both languages borrowed from the same source. But these overlaps are scattered and unpredictable, not enough to let a signer in one language piece together meaning in the other.
Regional Dialects Within Each Language
Both BSL and ASL have significant internal variation. BSL’s regional dialects are especially well documented. A large research project that filmed 249 deaf people across eight UK cities (London, Bristol, Birmingham, Manchester, Newcastle, Glasgow, Cardiff, and Belfast) confirmed strong regional vocabulary differences. The researchers found around 17 different BSL signs for the color “purple.” Signs for numbers one through 20 vary so much that Manchester has a number system unlike any other city in the UK. Even the sign for “green” differs between Glasgow and Cardiff.
These dialects developed largely through the residential schools for the deaf that existed in different parts of the country. Children who grew up at a particular school absorbed its local signing style, and those patterns persisted across generations. ASL has its own regional and cultural variations across the United States, shaped by similar patterns of deaf school communities and geographic separation.
Legal Recognition
BSL gained formal legal recognition in the UK through the British Sign Language Act 2022, which officially acknowledges it as a language of England, Wales, and Scotland. This was a landmark moment for the UK’s deaf community, where over 70,000 people use BSL as their first language. That said, the Act doesn’t require organizations to provide BSL interpretation or make it a mandatory part of anti-discrimination accommodations. It’s a recognition of status rather than an enforcement mechanism.
ASL does not have equivalent standalone federal legislation in the United States. It is widely recognized as a legitimate language in practice. Most US states accept ASL courses for foreign language credit in schools and universities, and federal disability laws require reasonable communication accommodations, which often means ASL interpretation. But there is no single “ASL Act” equivalent to the UK’s 2022 law.
Can BSL and ASL Signers Communicate?
Not easily. The two languages differ in alphabet, vocabulary, and grammar. A BSL signer meeting an ASL signer for the first time would face a genuine language barrier, comparable to a Portuguese speaker trying to converse with someone who only speaks Japanese. With time and patience, signers from different languages can sometimes use gesture, context, and a shared understanding of visual communication to get basic ideas across. But fluent conversation requires learning the other language, just as it would with any two unrelated spoken languages.
There are over 300 sign languages used around the world. The assumption that sign language is universal is one of the most common misunderstandings hearing people hold. Each deaf community developed its own language shaped by local history, schools, and culture. BSL and ASL just happen to be two of the most widely known examples of how different those paths can be.