Schopenhauer used to compare the obscure and continuous effort of the unconscious, in the midst of impressions imprisoned in the memory, to rumination. This rumination, which is purely physiological, may suffice to modify convictions or beliefs. Hartmann discovered that a hostile idea, at first brushed aside, succeeded, after a certain time, in supplanting in his mind the idea which he was accustomed to entertain of man or of a fact: "If you wish or have the occasion to express your opinion upon the same subject, after days, weeks, or even months, you discover, to your great surprise, that you have undergone a veritable mental revolution--that you have completely abandoned opinions which, up to that time, you had firmly believed to be yours, and that new ideas have completely taken their place. I have often noted this unconscious processus of digestion and mental assimilation in my own case, and have always instinctively refrained from disturbing the process by premature reflection, whenever it involved important questions affecting my conceptions of the world and of the mind."[6] This observation might be extended to the exceedingly interesting problem of conversion. There is no doubt that people have suddenly felt themselves brought, or brought back, to religious ideas, when they had neither wish nor fear nor hope for this change. In conversion the will can act only after a long effort on the part of the subconscious, and when all the elements of the new conviction have been secretly assembled and combined. This new force, which supports the convert, and whose origin is unknown to him, is what theology calls grace. Grace is the result of a subconscious effort. Grace is subconscious.