Abstract
This paper addresses the problem of evil from the perspective of saint Thomas Aquinas. It is argued that the nature of moral evil is in the individual who for some reason lost it departs from the pursuit of the good that is inherent to being. Synderesis is the only indissoluble bridge that man has with natural law and even with eternal. Converted into noluntas will guide man intrinsically evil acts but the synderesis, as a power with a natural habit, is the best guide for the contingent decision-making under the rubric of the first practical principles from transcendent.