There is no universal sign language since sign languages have their origin in the different deaf communities that exist around the world, and they developed independently of each other. Consequently, there are naturally differences between these languages – in the lexicon and in the grammar. Hearing people often do not realize that sign languages have a natural origin but think rather that they have been invented by teachers of the deaf. They then argue that the inventors should have created one form of sign language for convenience. This is based on a misunderstanding.