A fugue begins with the exposition of its subject in one of the voices alone in the tonic key. After the statement of the subject, a second voice enters and states the subject with the subject transposed to another key (usually the dominant or subdominant), which is known as the "answer". To make the music run smoothly, it may also have to be altered slightly. When the answer is an exact copy of the subject to the new key, with identical intervals to the first statement, it is classified as a "real answer"; if the intervals are altered to maintain the key it is a "tonal answer".