if is the set of all strings that machine accepts, we say that is the language of machine and write . we say that recognizes or that accepts . because the term accept has different meanings when we refer to machines accepting strings and machines accepting languages, we prefer the term recognize for languages in order to avoid confusion.
a machine may accept several strings, but it always recognizes only one language. if the machine accepts no strings, it still recognizes one language–namely, the empty language .