The basic distinction in the whole realm of human thought is that between the self and the not-self. It is here that the baby begins as he takes his first steps in human reasoning— first steps which may be the start of a road leading to the highest pinnacles of philosophical reflexion. So the Christian Church from the very start of her life found herself forced to articulate her beliefs and practices over against the non-Christian environment in which she was set. In the course of distinguishing between the self and the not-self the baby pays particular attention to those things which appear to stand somewhere on the borderland between the two—the extremities of his body, his fingers and toes, and the gloves and socks which he finds so closely associated with them. So also with the Church: it was those who stood on the borderland between her and the distinctively non-Christian environment outside who demanded the closest attention. It was in grappling with the heretic, the would-be Christian whom she was unwilling to recognize, that the Church was forced to articulate her beliefs with an ever-increasing measure of precision. It is only as the child grows up that he begins to indulge in reasoning as a conscious activity undertaken for its own sake in comparative detachment from the stimulus of immediate need.