Christian theology draws its concept of evil from the Old and New Testaments. The Christian Bible exercises "the dominant influence upon ideas about God and evil in the Western world." In the Old Testament, evil is understood to be an opposition to God as well as something unsuitable or inferior such as the leader of the fallen angels Satan In the New Testament the Greek word "poneros" is used to indicate unsuitability, while "kakos" is used to refer to opposition to God in the human realm. Officially, the Catholic Church extracts its understanding of evil from its canonical antiquity and the Dominican theologian, Thomas Aquinas, who in "Summa Theologica" defines evil as the absence or privation of good. French-American theologian Henri Blocher describes evil, when viewed as a theological concept, as an "unjustifiable reality. In common parlance, evil is 'something' that occurs in the experience that "ought not to be"."