Character being, as we have seen above, a habit, and virtue, on the other hand, being also a habit, the problem which presents itself to him who wishes to improve his character and exchange his vices for virtues, is to know how one habit may be substituted for another, and how even a painful habit may be substituted for an agreeable habit, sometimes for a habit which has lost its charm, but not yet its empire over one. This problem may be found analyzed and most pathetically described in the _Confessions_ of St. Augustine: "I was," he tells us, "like those who wish to get awake, but who, overcome by sleep, fall back into slumber. There is certainly no one who would wish to sleep always, and who would not rather, if he is healthy of mind, prefer the waking to the sleeping state; and yet there is nothing more difficult than to shake off the languor which weighs our limbs down; and often, though the hour for waking has come, we are against our will made captives by the sweetness of sleep.... I was held back by the frivolous pleasures and foolish vanities which I had found in the company of my former friends: they hung on the vestures of my flesh, whispering, 'Art thou going to abandon us?'... If, on the one hand, virtue attracted and persuaded me, pleasure on the other captivated and enslaved me.... I had no other answer for the former, than: 'Presently, presently, wait a little.' But this 'presently' had no end and this 'wait a little' was indefinitely prolonged, Wretch that I am! who will deliver me from the body of this death?"[160] At so painful a juncture, the Christian religion offers its children an all-powerful and efficacious remedy: this is what it calls _grace_. But of this means moral philosophy cannot dispose; all it can do is to find in the study of human nature the exclusively natural means God has endowed it with, to elevate man to virtue. Now, these means, limited though they be, should not be considered inefficient, since for many centuries they sufficed the greatest men and sages of antiquity.[161] =179. Rules of Malebranche and Aristotle.=--We may take for a starting point this maxim of Malebranche, which he borrowed from Aristotle: _Acts produce habits, and habits produce acts_.[162] A habit, in fact, is induced by a certain number of often repeated actions; and once generated, it produces in its turn acts, so to say, spontaneous and without any effort of the will. Thence spring vices and virtues; and the problem is to know how the first may be corrected, and the second retained: for the question is not only to pass from evil to good, but we should also take care not to slide from good into evil.