Let us take first the case of a man forming the habit of turning out the basement light. It usually happens that when a man has an electric light in the basement of his house, it is hard for him at first to think to turn out the light at night when he retires, and as a consequence the light often burns all night. This is expensive and unnecessary, so there is a strong incentive for the man to find a plan which will insure the regular turning-off of the light at bedtime. The plan usually hit upon is the following: The electric switch that controls the basement light is beside the basement stairway. The man learns to look at the switch as he comes up the stairs, after preparing the furnace fire for the night, and learns to take hold of the switch when he sees it and turn off the light. Coming up the stairs means to look at the switch. Seeing the switch means to turn it. Each step of the performance touches off the next. The man sees that in order to make sure that the light will always be turned off, the acts must all be made automatic, and each step must touch off the next in the series. At first, the man leaves the light burning about as often as he turns it off. After practicing for a time on the scheme, the different acts become so well connected that he seldom leaves the light burning. We say that he has formed the _habit_ of turning off the light. For a second illustration, let us take the process of learning that nine times nine equals eighty-one. At first, one does not say or write "eighty-one" when one sees "nine times nine," but one can acquire the habit of doing so. It does not here concern us how the child learns what the product of nine times nine is. He may learn it by counting, by being told, or by reading it in a book. But however he first learns it, he fixes it and makes it automatic and habitual by _continuing_ to say or to write, "nine times nine equals eighty-one." The essential point is that at first the child does not know what to say when he hears or sees the expression "nine times nine," but after long practice he comes to give automatically and promptly the correct answer. For the definite problem "nine times nine" there comes the definite response "eighty-one." For a third illustration, let us take the case of a man tipping his hat when he meets a lady. A young boy does not tip his hat when he meets a lady until he has been taught to do so. After he learns this act of courtesy he does it quite automatically without thinking of it. For the definite situation, meeting a lady of his acquaintance, there comes to be established the definite response, tipping the hat. A similar habit is that of turning to the right when we meet a person. For the definite situation, meeting a person on the road or street or sidewalk, there is established the definite response, turning to the right. The response becomes automatic, immediate, certain.