The other objection that it is impossible to establish a "reasonable" relation between individual and social well-being arises from a dual confusion as to what is the proper sphere of ethics, and of the mutual relation of the individual and society. To take an individual and ask, "Why should he act so as to promote the general welfare?" is to imply that ethical rules may have an application to man out of relation with his fellows. That, we have already seen, is quite wrong, since moral rules fail to be intelligible once we separate man from his fellows. Discussing ethics while leaving out social life is like discussing the functions of the lungs and leaving out of account the existence of an atmosphere. If, then, instead of treating the individual and society as two distinct things, either of which may profit at the expense of the other, we treat them as two sides of the same thing, each an abstraction when treated alone, the problem is simplified, and the solution becomes appreciably easier. For the essential truth here is that just as there is no such thing as a society in the absence of the individuals composing it, so the individual, as we know him, disappears when we strip him of all that he is in virtue of his being a part of the social structure. Every one of the characteristic human qualities has been developed in response to the requirements of the social medium. It is in virtue of this that morality has anything of an imperative nature connected with it, for if man is, to use Sir Leslie Stephen's phrase, a cell in the social tissue, receiving injury as the body social is injured, and benefitting as it is benefitted, then the refusal of a man to act so that he may promote the general welfare can be shown to be unreasonable, and also unprofitable to the individual himself. In other words, our efficiency as an individual must be measured in terms of our fitness to form part of the social structure, and consequently the antithesis between social and personal well-being is only on the surface. Deeper knowledge and a more exact understanding reveals them as two sides of the same fact.