What is a sign language and how do sign languages develop? 

Where spoken languages rely on sounds that Deaf people cannot hear to express concepts, sign languages rely on complex and linguistically significant combinations of hand motions, body movements and facial expressions. The visual nature of sign languages makes them a natural means of communication for Deaf communities. Sign languages are capable of communicating a full range of meaning, just as spoken languages do. Often, signs may visually depict in some way the ideas they represent, but an equal number of signs are completely arbitrary. Some sign languages utilize manual alphabets to spell out proper names or borrow spoken language terms. Spoken language grammars are linear (normally just one idea presented at a time). In contrast, sign language grammars are spatial—a number of ideas can be expressed simultaneously and the relative placement of people and places is depicted directly in the space around the signer. Sign languages have developed naturally over time through Deaf people communicating with each other, just as spoken languages originated naturally through hearing people speaking with each other. 

Why is the word “Deaf” capitalized? What does that mean? 

When capitalized, “Deaf” refer to a linguistic-cultural group, whereas deaf with a “lower case d” refers to the audiological condition. Deaf people are a distinct group culturally from those who are hard of hearing or those who employ oral means of communication and identify more closely with the hearing community. Much as someone who was born in Sweden and speaks Swedish as his or her first language is recognized as Swedish, so a person who is physically deaf, uses a sign language as his or her first language, and is part of the Deaf community, is a Deaf person. Not all writers use this convention, however. Some prefer to use lower-case all the time, and use other means to distinguish the two concepts

In the USA only about 5% of the Deaf population is born to Deaf parents. As a result, the transmission of sign language usually occurs through peers, not parents. The Deaf community places a high value on interaction with other Deaf people as a means of processing and internalizing information. Gathering at Deaf schools, clubs, associations and churches plays an important role in their social and information-gathering life. Informal interaction in such settings is the primary way that sign languages are passed on from one generation to the next. In these contexts, a Deaf culture emerges that expresses uniquely Deaf values, customs, world views, and approaches to communication.

How many different sign languages are used by Deaf people? 

Linguists have identified more than 130 sign languages worldwide, and SIL estimates that the actual number may exceed 400. Generally, these sign languages are named after the countries in which their communities reside. There are Egyptian Sign Language, Cuban Sign Language and Ghanaian Sign Language—and so on. Some are specific to regions or cities within the same country. For example, there are Haiphong Sign Language and Hanoi Sign Languages within the country of Vietnam. In other cases, totally unrelated sign languages have arisen in different countries that otherwise share the same spoken language—as is the case for British Sign Language and American Sign Languages. In other words, there is no correlation between the local/national spoken language and any sign languages that may have developed in the same location.