description was _Lex_ or _Jus Gentium_. That is to say, it was not to be considered as a primitive law which lay embedded like first principles in human nature; but that it was what the nations had derived from primitive principles, not by any force of logic, but by the simple evolution of life. The human race had found by experience that the observance of the natural law entailed as a direct consequence the establishment of certain institutions. The authority, therefore, which these could boast was due to nothing more than the simple struggle for existence. Among these institutions were those same three (civil authority, slavery, private property), which the Fathers had come to justify by so different a method of argument. Thus, by the late Roman lawyers private property was upheld on the grounds that it had been found necessary by the human race in its advance along the road of life. To our modern ways of thinking it seems as though they had almost stumbled upon the theory of evolution, the gradual unfolding of social and moral perfection due to the constant pressure of circumstances, and the ultimate survival of what was most fit to survive. It was almost by a principle of natural selection that mankind was supposed to have determined the necessity of civil authority, slavery, private property, and the rest. The pragmatic test of life had been applied and had proved their need. A third powerful influence in the development of Christian social teaching must be added to the others in order the better to grasp the mental attitude of the mediaeval thinkers. This was the rise and growth of monasticism. Its early history has been obscured by much legendary detail; but there is sufficient evidence to trace it back far into the beginnings of Christianity. Later there had come the stampede into the Thebaid, where both hermit life and the gathering together of many into a community seem to have been equally allowed as methods of asceticism. But by the fifth century, in the East and the West the movement had been effectively organised. First there was the canonical theory of life, introduced by St. Augustine. Then St. Basil and St. Benedict composed their Rules of Life, though St. Benedict disclaimed any idea of being original or of having begun something new. Yet, as a matter of fact, he, even more efficiently than St. Basil, had really introduced a new force into Christendom, and thereby became the undoubted father of Western monasticism.