Habits may be profitably compared to physiological functions, like breathing, digesting. The latter are, to be sure, involuntary, while habits are acquired. But important as is this difference for many purposes it should not conceal the fact that habits are like functions in many respects, and especially in requiring the cooperation of organism and environment. Breathing is an affair of the air as truly as of the lungs; digesting an affair of food as truly as of tissues of stomach. Seeing involves light just as certainly as it does the eye and optic nerve. Walking implicates the ground as well as the legs; speech demands physical air and human companionship and audience as well as vocal organs. We may shift from the biological to the mathematical use of the word function, and say that natural operations like breathing and digesting, acquired ones like speech and honesty, are functions of the surroundings as truly as of a person. They are things done _by_ the environment by means of organic structures or acquired dispositions. The same air that under certain conditions ruffles the pool or wrecks buildings, under other conditions purifies the blood and conveys thought. The outcome depends upon what air acts upon. The social environment acts through native impulses and speech and moral habitudes manifest themselves. There are specific good reasons for the usual attribution of acts to the person from whom they immediately proceed. But to convert this special reference into a belief of exclusive ownership is as misleading as to suppose that breathing and digesting are complete within the human body. To get a rational basis for moral discussion we must begin with recognizing that functions and habits are ways of using and incorporating the environment in which the latter has its say as surely as the former. We may borrow words from a context less technical than that of biology, and convey the same idea by saying that habits are arts. They involve skill of sensory and motor organs, cunning or craft, and objective materials. They assimilate objective energies, and eventuate in command of environment. They require order, discipline, and manifest technique. They have a beginning, middle and end. Each stage marks progress in dealing with materials and tools, advance in converting material to active use. We should laugh at any one who said that he was master of stone working, but that the art was cooped up within himself and in no wise dependent upon support from objects and assistance from tools.