The leading traits of a code, under which complete living through voluntary co-operation is secured, may be simply stated. The fundamental requirement is that the life-sustaining actions of each shall severally bring him the amounts and kinds of advantage naturally achieved by them, and this implies firstly that he shall suffer no direct aggressions on his person or property, and, secondly, that he shall suffer no indirect aggressions by breach of contract. Observance of these negative conditions to voluntary co-operation having facilitated life to the greatest extent by exchange of services under agreement, life is to be further facilitated by exchange of services beyond agreement: the highest life being reached only when, besides helping to complete one another's lives by specified reciprocities of aid, men otherwise help to complete one another's lives. CHAPTER IX. CRITICISMS AND EXPLANATIONS. § 56. Comparisons of the foregoing chapters, with one another, suggest sundry questions which must be answered partially, if not completely, before anything can be done toward reducing ethical principles from abstract forms to concrete forms. We have seen that to admit the desirableness of conscious existence is to admit that conduct should be such as will produce a consciousness which is desirable--a consciousness which is as much pleasurable and as little painful as may be. We have also seen that this necessary implication corresponds with the _à priori_ inference, that the evolution of life has been made possible only by the establishment of connections between pleasures and beneficial actions, and between pains and detrimental actions. But the general conclusion reached in both of these ways, though it covers the area within which our special conclusions must fall, does not help us to reach those special conclusions. Were pleasures all of one kind, differing only in degree; were pains all of one kind, differing only in degree; and could pleasures be measured against pains with definite results, the problems of conduct would be greatly simplified. Were the pleasures and pains serving as incentives and deterrents, simultaneously present to consciousness with like vividness, or were they all immediately impending, or were they all equi-distant in time; the problems would be further simplified. And they would be still further simplified if the pleasures and pains were exclusively those of the actor. But both the desirable and the undesirable feelings are of various kinds, making quantitative comparisons difficult; some are present and some are future, increasing the difficulty of quantitative comparison; some are entailed on self and some are entailed on others; again increasing the difficulty. So that the guidance yielded by the primary principle reached is of little service unless supplemented by the guidance of secondary principles.