Materialism is the position in philosophy, standing in opposition to idealism, which asserts the ontologic primacy of matter. In psychology, materialism is any theory denying the existence of mind and regarding mental phenomena to be the mere outworking of purely physico-mechanical processes in the brain. In the philosophy of religion, materialism is any synthesis denying the existence of an immortal human soul. The earliest thoroughgoing materialists were the classical Atomists (see atomism), in particular Democritus and Lucretius. The growth of modern science brought a revival of materialism, which many have argued is a prerequisite for scientific thought, particularly in the field of psychology. Other philosophers, however, have argued against this view, recognizing the arbitrariness of the materialist hypothesis.