... sign language involves much more than bare handshapes. In signing, tenses, adjectives and all the little "glue" words which make speech fluent are inserted not as extra handshapes but in other ways, such as the use that signers make of the space around them. For example, a gesture made up behind the ear puts a word into the past tense. The same gesture made in varying positions out in front will span a time-line that runs from the present into the future.
Deaf people also use this sign space as if it were a stage on which they enact the story they are telling. For instance, when a signer mentions an object, such as the driver of a car, it is "left behind" in a certain position in this gestural space. To refer back to the driver, even some sentences later, there is no need to repeat the sign driver as merely bringing the hands back to the original spot is enough to remind the listener as to what or whom is being spoken about.
The only real difference between sign and speech is that whereas in spoken language, words have to be strung together in sequence, sign allows whole phrases to be expressed in one go, the various parts being scattered around in sign space. This compression is important because it takes roughly twice as long to move the hands into a sign shape as it does to speak a word. By, in effect, speaking in phrases rather than words, sign overcomes this built-in speed disadvantage and so happily can match the pace of speech. Not only has sign got the speed and grammatical complexity of spoken language, it is also a fully symbolic form of communication.