principle of demonstration is the self-evident principle of noncontradiction ("the same thing cannot be affirmed and denied at the same time"), the first principle of action is the self-evident Bonum precept ("good is to be done and pursued and evil avoided"). This natural law precept prescribe doing and pursuing what reason knows is good while avoiding evil. Reason knows what is objectively good because the good is naturally beneficial and evil is the contrary. To explain goods that are naturally self-evident, Aquinas divides them into three categories: substantial goods of self-preservation desired by all; the goods common to both animals and humans, such as procreation and education of offspring; and goods characteristic of rational and intellectual beings, such as living in community and pursuing the truth about God. To will such natural goods to oneself and to others is to love. Accordingly, Aquinas states that the love precept obligating loving God and neighbor are "the first general principles of the natural law, and are self-evident to human reason, either through nature or through faith. Wherefore all the precepts of the decalogue are referred to these, as conclusions to general principles." To so focus on lovingly willing good is to focus natural law on acting virtuously. In his Summa Theologiae, Aquinas wrote: Thomas emphasized that "Synderesis is said to be the law of our mind, because it is a habit containing the precepts of the natural law, which are the first principles of human actions." According to Thomas "...all acts of virtue are prescribed by the natural law: since each one's reason naturally dictates to him to act virtuously. But if we speak of virtuous acts, considered in themselves, i.e., in their proper species, thus not all virtuous acts are prescribed by the natural law: for many things are done virtuously, to which nature does not incline at first; but that, through the inquiry of reason, have been found by men to be conducive to well living." Therefore, we must determine if we are speaking of virtuous acts as under the aspect of virtuous or as an act in its species. Thomas defined the four cardinal virtues as prudence, temperance, justice, and fortitude. The cardinal virtues are natural and revealed in nature, and they are binding on everyone. There are, however, three theological virtues: faith, hope, and charity. Thomas also describes the virtues as imperfect (incomplete) and perfect (complete) virtues. A