This paper discusses one of the greatest doctors of the Catholic Church, St. Thomas Aquinas. He says that evil is not an essence, form or substance, which goodness possesses. Rather it is the absence of that goodness, or the "privation of good (Aquinas). God creates a created thing or creature for a purpose and that purpose is necessarily good, because God created it, and that creature's nature is directed at that purpose, which is good. When the creature, by his or her own free will, decides not to opt for that purpose - directly or indirectly - he or she violates his or her own nature, which is aimed or directed towards his or her own good, and therefore, commits evil. It is through the vehicle of the human will, which is free, that evil occurs. But evil has no purpose or substance of its own, because and therefore God did not create it. Neither does He allow it. It exists only because the human will, which is free, opts for it.
