Bahya's division is identical with neither the one nor the other. Ethical practice may be purely external and a matter of the limbs, quite as much as sacrifice and ceremonial ritual. On the other hand, one may feel profoundly moved with the spirit of true piety, love of God and loyalty to his commandments in the performance of a so-called "traditional commandment," like the fastening of a "mezuzah" to the door-post. Bahya finds room for Saadia's classification but it is with him of subordinate importance, and is applicable only to the "duties of the limbs." Among these alone are there some which the reason unaided by revelation would not have prescribed. The "duties of the heart" are all rational. Like all precepts they are both positive and negative. Examples of positive duties of the heart are, belief in a creator who made the world out of nothing; belief in his unity and incomparability; the duty to serve him with all our heart, to trust in him, to submit to him, to fear him, to feel that he is watching our open and secret actions, to long for his favor and direct our actions for his name's sake; to love those who love him so as to be near unto him, and to hate those who hate him. Negative precepts of this class are the opposites of those mentioned, and others besides, such as that we should not covet, or bear a grudge, or think of forbidden things, or desire them or consent to do them. The common characteristic of all duties of the heart is that they are not visible to others. God alone can judge whether a person's feeling and motives are pure or the reverse. That these duties are incumbent upon us is clear from every point of view. Like Saadia Bahya finds the sources of knowledge, particularly of the knowledge of God's law and religion, in sense, reason, written law and tradition. Leaving out the senses which are not competent in this particular case, the obligatory character of the duties of the heart is vouched for by the other three, reason, law, tradition. From reason we know that man is composed of soul and body, and that both are due to God's goodness. One is visible, the other is not. Hence we are obliged to worship God in a two-fold manner; with visible worship and invisible. Visible worship represents the duties of the limbs, such as prayer, fasting, charity, and so on, which are carried out by the visible organs. The hidden worship includes the duties of the heart, for example, to think of God's unity, to believe in him and his Law, to accept his worship, etc., all of which are accomplished by the thought of the mind, without the assistance of the visible limbs. Besides, the duties of the limbs, the obligation of which no one doubts, are incomplete without the will of the heart to do them. Hence it follows that there is a duty upon our souls to worship God to the extent of our powers.