which, in every society, must be fulfilled to a considerable extent before it can hold together; and which must be fulfilled completely before social life can be complete. Each citizen has to carry on his activities in such ways as not to impede other citizens in the carrying on of their activities more than he is impeded by them. That any citizen may so behave as not to deduct from the aggregate welfare, it is needful that he shall perform such function, or share of function, as is of value equivalent at least to what he consumes; and it is further needful that, both in discharging his function and in pursuing his pleasure, he shall leave others similarly free to discharge their functions and to pursue their pleasures. Obviously, a society formed of units who cannot live, without mutual hindrance, is one in which the happiness is of smaller amount than it is in a society formed of units who can live without mutual hindrance. And obviously the sum of happiness in such a society is still less than that in a society of which the units voluntarily aid one another.
Now, under one of its leading aspects, civilization is a process of developing in citizens a nature capable of fulfilling these all-essential conditions; and, neglecting their superfluities, laws and the appliances for enforcing them are expressions and embodiments of these all-essential conditions. On the one hand, those severe systems of slavery, and serfdom, and punishment for vagabondage, which characterized the less-developed social types, stand for the necessity that the social unit shall be self-supporting. On the other hand, the punishments for murder, assault, theft, etc., and the penalties on breach of contract, stand for the necessity that, in the course of the activities by which he supports himself, the citizen shall neither directly injure other citizens, nor shall injure them indirectly, by taking or intercepting the returns their activities bring. And it needs no detail to show that a fundamental trait in social progress is an increase of industrial energy, leading citizens to support themselves without being coerced in the harsh ways once general; that another fundamental trait is the progressive establishment of such a nature in citizens that, while pursuing their respective ends, they injure and impede one another in smaller degrees; and that a concomitant trait is the growth of governmental restraints which more effectually check the remaining aggressiveness. That is to say, while the course of civilization shows us a clearer recognition and better enforcement of these essential conditions, it also shows us a gradual moulding of humanity into correspondence with them.
Along with the proofs thus furnished that the biological law of adaptation, holding of all other species, holds of the human species, and that the change of nature undergone by the human species since societies began to develop, has been an adaptation of it to the conditions implied by harmonious social life, we receive the lesson, that the one thing needful is a rigorous maintenance of these conditions. While all see that the immediate function of our chief social institutions is
