Now is a good time to ask. During most of the
20th century, no one really knew. Not even Deaf
people who used sign language in their daily lives
knew what it was. Those who noticed that many
thoughts are expressed differently in sign and in
English assumed that sign was an ungrammatical
form of English. Most Americans thought it was
a way to express English words with signs—a
substitute for speech. As the truth came to light
in the second half of the 20th century, it surprised
everyone.