=How Habits Are Formed.= It is clear from the foregoing discussion that the essential thing in a habit is the definiteness of the connection between the stimulus and the response, between the situation and the reaction to the situation. Our question now is, how is this definiteness of connection established? The answer is, _through repetition_. Let us work the matter out from a concrete case, such as learning to play the piano. In piano playing the stimulus comes from the music as printed on the staff. A note having a certain position on the staff indicates that a certain key is to be struck. We are told by our music teacher what keys on the piano correspond to the various notes on the staff, or we may learn these facts from the instruction book. It makes no difference how we learn them; but after we know these facts, we must have practice to give us skill. The mere knowledge will not make us piano players. In order to be skillful, we must have much practice not only in striking the keys indicated by the various note positions, but with the various combinations of notes. For example, a note on the second space indicates that the player must strike the key known as "A." But "A" may occur with any of the other notes, it may precede them or it may follow them. We must therefore have practice in striking "A" in all these situations. To have skill at the piano, we must mechanize many performances. We must be able to read the notes with accuracy and ease. We must practice so much that the instant we see a certain combination of notes on the staff, our hands immediately execute the proper strokes. Not only must we learn what keys on the piano correspond to the various notes of the music, but the notes have a temporal value which we must learn. Some are to be sounded for a short time, others for a longer time. We have eighth notes, quarter notes, half notes, etc. Moreover, the signature of the music as indicated by the sharps or flats changes the whole situation. If the music is written in "A sharp" then when "A" is indicated on the staff, we must not strike the white key known as "A," but the black key just above, known as "A sharp." Briefly, in piano playing, the stimulus comes from the characters printed on the staff. The movements which these characters direct are very complicated and require months and years of practice. We must emphasize the fact that practice alone gives facility, years of practice. But after these years of practice, one can play a piece of music at sight; that is, the first stimulus sets off perfectly a very complicated response. This sort of performance is one of the highest feats of skill that man accomplishes.