Book IV examines the problem of evil's existence. Boethius has listened to and agreed with all of the arguments Philosophy has so far presented. But if God is perfect in his goodness, and is the unity of all things rules the world, how is it that evil is allowed to exist and is not always punished? In addition, where wickedness flourishes, virtue is often downtrodden and even stamped out. If God is omniscient and omnipotent and beneficent how can this evil continue in His world?
Lady Philosophy reminds Boethius of his catechism - that God has said no evil will go unpunished, no virtue will be forgotten. Philosophy also asserts that the wicked are weak and have no power, and the virtuous are strong and powerful.
All people strive to true happiness; the wicked cannot possibly attain it, and the virtuous can attain it. The evil people of the world seek happiness in misguided ways, and they will never attain their goal. Evil people are excluded from attaining the supreme good of perfect happiness, and therefore they are excluded from all that really exists. Since they cannot possibly attain the only thing of value (true happiness) any earthly power they have (which is, as explained in Book II, only ever power over possessions and bodies of people, not their minds or souls) is not actually power at all. Evil people, Philosophy says, cease to exist. The wicked lose power and strength by striving for things that do not matter. They also lose their humanity, and become like the animals they represent by their various desires (the glutton becomes pig-like, the lazy are asses).
Boethius agrees, but he laments that the wicked harm the virtuous and are not punished. Wickedness, like virtue, Philosophy assures Boethius, is its own reward. The wicked, by the fact of their very wickedness, are rewarded by their lack of existence and their descent into bestiality. The are, by their own actions rather than by any outside punishment, denied happiness. If they are punished, the evil people of the world are given a good, for they have a chance at redeeming themselves and changing their ways. When the evil people of the world escape punishment, their capacity and likelihood for more wickedness increases.
Boethius finds this difficult, and protests. He can't abide that the good must suffer the earthly punishments that the evil, who deserve them, inflict upon them. This is acceptable in a world where nothing is determinate, but our world, he says, is ruled by God. How can God in his omnipotence allow this?
The following argument for the foreknowledge (or Providence) of God is famous and somewhat difficult. Philosophy agrees that this is indeed a mystery, and no human being can hope to understand it fully.
All events on Earth are happening in the unchanging mind of God, for whom there is no past, present or future. Since we are temporal beings, we cannot understand how everything that has ever happened or will happen is happening for God simultaneously, but every occurrence is contained within His mind. The government of all changeable things is called Providence. When this is applied in the temporal realm, it is called by the old pagan name of Fate. In short, Providence represents the foreknowledge of God of all things, and controls of the nature of all things. The actual connection of events which occur on Earth is Fate. Providence is the divine reason by which the world is ordered. Fate is the same reason when applied the temporal world. Because we on earth cannot understand Providence, Fate sometimes seems unordered and cruel.
Because of this, anything that happens to you, good fortune or bad, is good, because if your fortune is bad it is an instruction toward virtue. This is, in short, the best of all possible worlds, for evil doesn't actually have any substance or power, and all the events of the world have been planned by Providence.
This discussion of evil in the world - this theodicy - is one of the most famous and important passages of this book. The argument that evil has no substance and does not exist is not always considered an orthodox Catholic idea, but it breaks no rules of the catechism and is easier to prove logically than the existence of the devil. The fact that the omniscience, omnipotence, and beneficence of God is retained is the important point here, and Boethius does it with verve and daring.
Some critics have read the seed of fascism in the idea that the truly wicked are no longer human but have become animals. Some fascist states, such as Nazi Germany, similarly contended that the "wicked" are not really human. In Boethius' defense, Lady Philosophy advises compassion toward the wicked, rather than contempt, an idea that is never part of fascist philosophy. However, Philosophy does continue by saying that we should punish the wicked as a cure for their wickedness. Boethius never really examines the human social context that is an inevitable part of determining who is "wicked" and who isn't. If human beings, who are inevitably flawed and cannot understand the true nature of good and evil, take it upon themselves to punish the "wicked" among them, surely injustice may result. Critics have also said that it is possible that Boethius' injunction to purge the wicked justified torture and death for heretics, in order to enable them to "lay aside the filth of vice through the pains of punishment." Again, Boethius does not directly address the difficulty of locating absolute values like "vice" and "virtue" among inevitably flawed, imperfect human beings. Certainly Boethius foreshadows the extremes of the Inquisition and the mass slaughter of Jews and other "heretics" at the hands of Christians.
Boethius' argument that evil does not have any substance is not his own idea. Various philosophies and religions, including Neo-Platonism, had argued this idea before. The way Philosophy explains it through the ineffectual actions of evil people follows from previous arguments she has presented to Boethius. Rather than starting with a cosmic idea of good and evil and the nature of God, she starts, as she has every argument so far, with practical discussions of what is done by human beings on earth. This is, after all, supposed to be a "consolation," not necessarily a cosmography. When Boethius to be able to start with something he knows - the actions of the virtuous and the evil here on earth - he is better able to find comfort in his situation. Perhaps this is the reason Boethius wrote this book to begin with - to explain to himself and others how he was able to, without resorting to the revealed knowledge of the Bible, reconcile himself to his fate.
Providence and Fate are perhaps the two most difficult concepts to understand in this book. Because so much of what Boethius says inspired by faith, the arguments for these concepts may seem flip or inadequate. The concept of God holding all events in his mind at one time, outside of the temporal world, and Fate being the ordering of events in the temporal world, is, in the understatement of Philosophy, a "mystery." This is as complete an explanation of it as can be found, however, outside of a theological text.
Accepting that all fortune is good, and that this is the best of all possible worlds, is as difficult for Boethius as it is for the rest of us. Perhaps few today would accept that bad fortune leads us toward virtue and good fortune leads us to vice. However, this argument comforts Boethius, and makes him more accepting of his fate. Indeed, the Consolation of Philosophy in general functions more as a guidebook for salvaging happiness in the most adverse conditions rather than a theological proof of God's existence or the necessity of evil. One might go so far as to say that Boethius' Lady Philosophy insists upon the existence of God simply because that belief is conducive to Boethius' consolation. Truth and pristine logic are not Boethius' object; resignation in the face of unjust realities is.