Arguably, the most difficult challenge facing philosophy, theology, and religion is the problem of evil. The problem can be framed in different ways, depending on the purpose of the discussion.

For example, one can argue that the existence of evil militates against the existence of God. “If one of two contraries be infinite, the other would be altogether destroyed. But the word “God” means that He is infinite goodness. If, therefore, God existed, there would be no evil discoverable, but there is evil in the world. Therefore, God does not exist.” (Aquinas, Saint Thomas. The “Summa Theologica” of St. Thomas Aquinas. 1917). It should be pointed out that Aquinas is not making this argument, but rather, he is anticipating an objection to God’s existence.

Nevertheless, the above argument can be utilized by atheists. However, the existence of evil is no safe haven for atheists either. Even if God does not exist, evil remains. Further damning for atheists is that in the absence of God, they have no objective claim to call anything evil.

From a theological perspective, it is tempting to offer God’s answer to Job and leave it at that. (See Job 38-40). The text is too long to quote here, but it essentially comes down to God pointing out that human knowledge is insufficient to understand God’s designs. There is, of course, much to recommend this response to suffering. No doubt, human beings as creatures cannot understand the works of God as the creator. Still, God’s response to Job may not be satisfying to the one suffering. So, how can we Catholics approach the issue of evil?

First, we must distinguish between evil actions and actions that are right and wrong. Is going through a stop sign evil? What about accessing your neighbor’s wireless connection for free? While most of us would agree that these acts are wrong, we would be less likely to consider them evil.

Unfortunately, the history of mankind is replete with events that almost defy efforts to categorize them. In 2005, Joseph Duncan murdered three members of a family, including a thirteen-year-old boy. All three were bound and beaten to death with a hammer. Mr. Duncan also kidnapped the couple’s two other children and tortured and raped them over a period of six weeks.

Perhaps even more incomprehensible is institutional evil. It is impossible, for example, to simply classify Nazi atrocities as “wrong.” Human experimentation, mass murders, and rape are all part of humanity’s legacy. Nor are these horrors ancient history. Hitler, Mao, Stalin, and the Rwandan genocide are all nightmares that have occurred in the past century.

There are four “responses” to the existence of evil. The first, mentioned above, is to conclude that God does not exist. This is a non sequitur, however. An atheistic worldview does not remove the presence of evil or wipe from history the horrors of the twentieth century. Moreover, as the historian Jeffrey Russell notes, “the atheist rulers such as Lenin, Hitler, Stalin, Mao Zedong, and Pol Pot tortured, starved and murdered more people in the twentieth century than all the combined religious regimes of the world during the previous nineteen centuries.” (Russell, Jeffrey Burton. Exposing Myths About Christianity. InterVarsity Press, 2012).

The second response is more theologically profound. It concludes that the presence of evil in the world indicates that God is not all good. There are two ways to address this argument. First, one can simply point to Scripture, which states that God is good (e.g., Psalm 100:5 and Mark 10:18). The second way is to argue from the nature of evil. Evil, by definition, is a lack or privation of what ought to exist. Since God exists necessarily (as the first cause of creation), He cannot be lacking in any perfection. The reason is that lack indicates something outside of oneself, and there cannot be anything independent of that which exists necessarily. Therefore, it is impossible for God not to be good.

Another approach is one taken by the followers of Manichaeism. Manichaeism posited that the universe was a battleground between the spiritual realm, which was considered good, and the material world, which was seen as evil. Manichaeism appears to contradict Scripture, however, and was deemed a heresy in the fourth century.

The final response to evil is to see it as an effort by the Devil to negate the will of God. Before proceeding with this concept, it is essential not to let human beings off the hook, so to speak. It is too easy for those who engage in evil acts to exclaim that the Devil made them do it. Humans have free will and are not pawns of Satan. Rather, we must admit that we are complicit in the terrors of this world. Still, evil as a power wielded by the Devil must be given as much consideration as Scripture allows.

One encounters the Devil very early in the Bible. The serpent that tempts Eve is generally considered to symbolize the Devil. Christ Himself confronts and is tempted by Satan. The Devil as the tempter is an essential biblical motif. If evil is a privation, then the ultimate evil is the negation of the will of God. The Devil seeks to accomplish this negation by tempting us to act in ways that contradict God’s will.

In a very real sense, we are born into a world at war. The struggles and violence that all of us witness in the physical realm are only manifestations of the war between God and the Devil that occurs in the spiritual realm. All of this may seem abstract, but for Catholics, the strategy of spiritual warfare is quite simple. One must cease from committing mortal sin and avoid the occult, both of which open our lives to the influence of the enemy.

The secular world often eschews the concepts of good and evil in favor of moral relativism. However, as Catholics, we must be able to accept the reality of evil if only to be on guard against it.