In his fifteenth year he was apprenticed to John Parker, a bookseller. At the close of his indentures in 1720, Baker went on a visit to John Forster, a relative, who had a deaf-mute daughter, then eight years old. As a successful therapist of deaf people, he went on to make money, by a system that he kept secret.[1] His work as therapist caught the attention of Daniel Defoe, whose youngest daughter Sophia he married in 1729.