American Sign Language (ASL) is a complex visual-spatial language that is used by the Deaf community in the United States and English-speaking parts of Canada. It is a linguistically complete, natural language. It is the native language of many Deaf men and women, as well as some hearing children born into Deaf families.
ASL shares no grammatical similarities to English and should not be considered in any way to be a broken, mimed, or gestural form of English. In terms of syntax, for example, ASL has a topic-comment syntax, while English uses Subject-Object-Verb. In fact, in terms of syntax, ASL shares more with spoken Japanese than it does with English. I have some information on Japanese Sign Language as well.
Some people have described ASL and other sign languages as “gestural” languages. This is not absolutely correct because hand gestures are only one component of ASL. Facial features such as eyebrow motion and lip-mouth movements as well as other factors such as body orientation are also significant in ASL as they form a crucial part of the grammatical system. In addition, ASL makes use of the space surrounding the signer to describe places and persons that are not present.
Sign languages develop specific to their communities and is not universal. For example, ASL is totally different from British Sign Language even though both countries speak English. Many people consider it a shame that there isn’t a universal sign language (see below), however it’s also a shame that there isn’t a universal spoken language, right? I personally enjoy seeing the great variety and diversity of languages and the first topic of conversation when I meet a Deaf person from another country is an exchange of vocabulary: “How do you sign this? How do you sign that?”
Interesting, however, American Sign Language shares many vocabulary terms with Old French Sign Language (LSF) because a French Deaf man, Laurent Clerc, was one of the first teachers of the Deaf in the U.S. in the nineteenth century. So if you know ASL, you’re better off taking a vacation in France than in England! But the French connection to America is rare, most sign languages develop independently and each country (and in some cases, each city) has their own sign language.
(bolded is mine)