However, rabbinical Judaism never followed Philo so far in the footsteps of Plato as to consider the body or the flesh the source of impurity and sin, or “the prison house of the soul.” This view is fundamental in the Paulinian system of other-worldliness. For the rabbis the sensuous desire of the body (_yezer_) is a tendency toward sin, but never a compulsion. The weakness of the flesh may cause a straying from the right path, but man can turn the desires of the flesh into the service of the good. He can always assert his divine power of freedom by opposing the evil inclination (_yezer ha ra_) with the good inclination (_yezer ha tob_) to overcome it.(650) In fact, the rabbis are so far from acknowledging the existence of a compulsion of evil in the flesh, that they point to the history of great men as proof that the highest characters have the mightiest passions in their souls, and that their greatness consists in the will by which they have learned to control themselves.(651) 5. In the light of modern science the whole theory separating body and soul falls to the ground, and the one connecting man more closely with the animal world is revived. In this connection we think of the idea which medieval thinkers adopted from Plato and Aristotle, that there is a substance of souls—_nefesh hahiyonith_—which forms the basic life-force of men and animals. Physiology and psychology reveal the interaction and dependence of body and soul in the lowest forms of animal life as well as in the higher forms, including man. The beginnings of the human mind must be sought once for all in the animal, just as the origin of the animal reaches back into the plant world. Indeed, Aristotle anticipates the discoveries of modern science, placing the vegetative and animal souls beside the spirit of man. Thus motion and sensibility form the lower boundary-line of the animal kingdom, and self-consciousness and self-determination are the criteria of humanity. Yet this very self-conscious freedom which forms man’s personality, his _ego_, lifts him into a realm of free action under higher motives, transcending nature’s law of necessity, and therefore not falling within the domain of natural science. Dust-born man, notwithstanding his earthly limitations, in spite of his kinship to mollusk and mammal, enters the realm of the divine spirit. In the Midrash the rabbis remark that man shares the nature of both animals and angels.(652) Admitting this, we feel that he is tied neither to heaven nor to the earth, but free to lift himself above all creatures or sink below them all.