Now, that recognition, without which the arrangement could not exist at all, required, relatively, a considerable mental effort, _due in the first instance to the failure of force_. If the slave-owner had had more effective means of physical coercion, and had been able to subdue his slave, he would not have bothered about agreement, and this embryo of human society and justice would not have been brought into being. And in history its development has never been constant, but marked by the same rise and fall of the two orders of motive; as soon as one party or the other obtained such preponderance of strength as promised to be effective, he showed a tendency to drop free agreement and use force; this, of course, immediately provoked the resistance of the other, with a lesser or greater reversion to the earlier profitless condition. 'This perpetual tendency to abandon the social arrangement and resort to physical coercion is, of course, easily explainable by the biological fact just touched on. To realise at each turn and permutation of the division of labour that the social arrangement was, after all, the best demanded on the part of the two characters in our sketch, not merely control of instinctive actions, but a relatively large ratiocinative effort for which the biological history of early man had not fitted him. The physical act of compulsion only required a stone axe and a quickness of purely physical movement for which his biological history had afforded infinitely long training. The more mentally-motived action, that of social conduct, demanding reflection as to its effect on others, and the effect of that reaction upon our own position and a conscious control of physical acts, is of modern growth; it is but skin-deep; its biological momentum is feeble. Yet on that feeble structure has been built all civilisation.