Book III, the central Book and the longest of the five, opens with Boethius enchanted by Philosophy's final song of Book II. Throughout The Consolation of Philosophy, Boethius tells us, Philosophy's songs have been accompanied by the most beautiful music, for music is Philosophy's "handmaid"
Boethius has become refreshed, and the compelling arguments of Book II have made him ready for more "cures" and "capable of facing the blows of Fortune." Philosophy then informs Boethius that the object of her next lecture will be true happiness. True and perfect happiness can only be achieved by the possession of the supreme good in which all goods are possessed. All human beings desire true happiness, but most are lead into error by desiring false, or temporal, goods.
Philosophy goes on to explain that what many in the world think of as good; freedom from want (wealth), respect (honor), power, or fame, or simply pleasure, or those with confused or combined desires, such as the desire for wealth for the sake of power and pleasure, or power for the sake of money and fame, and even those who desire a spouse and children for the pleasure they bring. Beauty and strength of the body confer power and renown, and is a form of those desires. All of these desires are for happiness, however. The problem arises when humanity treats these goods as the ultimate good or the path to happiness. The fallen state (original sin from the Garden of Eden) of man is such that he seeks happiness in these inferior, exterior, multiple goods, rather than the one supreme good of God.
Before, however, Boethius and Philosophy sing their closing hymn to God, the source of all happiness, Philosophy goes through each of the supposed goods of earth. Wealth, once attained, is a source of worry. Physical beauty and strength is an illusion, created by the other people's desire to see beauty in the body. Furthermore, physical beauty and strength are easily and quickly lost, by time and illness. A man in high office receives honor and respect, but the office does not confer wisdom or virtue on the holder. Often, Philosophy says, high office creates corruption and degrades rather than elevates the officeholder. Virtue has intrinsic value, which, once achieved, confers its worth to those who possess it, but the same is not true of high office. If a king or official has power, the constant acquisition of more power would bring more happiness. But there is no empire on earth which rules all of humanity, so the inherent lack of power in power itself confers unhappiness on those with power.
Philosophy begins Part VI of Book III with the admonition, "Fame, in fact, is a shameful thing, and so often deceptive." She argues that nothing is more shameful than unjust fame. Also, the fame of a human being can never be spread to all the people of the world, just as power can't be over all people. Nobility of family doesn't confer virtue, either, except in the negative sense it may incite the noble to not disgrace the memory of their ancestors.
Bodily pleasure is of the least concern to Philosophy. She views it with contempt, and says that its "pursuit is full of anxiety and its fulfillment full of remorse." It is unhealthful, and even the worthy pleasure of a spouse and children can also bring many woes. Because these goods are not perfect, they are unable to give perfect happiness to any human being.
Boethius and Lady Philosophy agree that any or all of these earthly goods cannot bring any measure of true happiness to anyone, and therefore continue their inquiry after the "sufficiency" which would satisfy humanity's desire for true happiness. Here begins Boethius's partial proof for the existence of God. Since Boethius and Philosophy agree that humanity desires true happiness, that standard means that a supreme good exists. Since Lady Philosophy has shown that none of the earthly goods are the supreme good, nor are all of them together the supreme good, something outside of the earth must be the supreme good.
Sufficiency is linked by Lady Philosophy to power, since the being who was sufficient in all things (no longer desiring anything) would be powerful enough to live apart from earthly concerns. Therefore, something that is sufficient would need nothing, want nothing, exhibit supreme powerful, and thus would be worthy of reverence. This being would be happy. Therefore, Lady Philosophy concludes, this being would be wholly sufficient, powerful, glorious, and would be revered.
All of these conditions for pure happiness go by various names, but they consist of the same substance. This one happy, sufficient being, Boethius implies, is God. The unity that God fulfills is the essence of the desire of all things. Boethius and Philosophy end Book III with a song asking for help in finding the true nature of happiness and God.
The "lack of completeness" argument for fame and power may seem flimsy to some modern readers. Where is the gratitude for what one has? Why, according to Boethius and Lady Philosophy, can't we be happy with some power and some fame, or, by extension some physical beauty or strength, or some wealth, even though we may not possess all of these things or for eternity or in their completeness. Why is not a measure of good things enough?
Boethius would argue that the incompleteness of these goods shows how imperfect as "goods" they really are. The attainment of any of these desires is merely a misdirected desire for true happiness in God, which is attainable in its complete and whole form. There are some holes in this argument, but, again, it is necessary to consider Boethius's dialogue within the context of his Christianity.
Why, for example, couldn't the attainment of some of the goods (some fame, some money, some physical strength) be a source of lasting or real happiness on earth, at least until death and the communion with God? Boethius sees that no human being is without further desires, and any acquisition of these earthly goods only incites people to want more of them. While some people may be "content" with the satisfaction of their basic needs, they are not made happy by the attainment of these earthly goods, but only by some spiritual source of happiness. So even those who are not particularly greedy or acquisitive are still not able to access happiness here on earth.
To some this may seem a pessimistic argument, and particularly damning of human nature. However, Boethius also considered that any happiness on earth would represent a denial of God, an idea he was unwilling to contemplate because he was a Christian - the suggestion that human beings can be fulfilled and happy apart from God is tantamount to blasphemy for Boethius.
The proof of God in this Book is considered partial by most theologians, and wasn't the focus of the book. Boethius takes for granted that there is a God, and that his readers agree with him. But the proof is based on the inadequacy of temporal desires, and is really a negative proof; because it is not earthly, it must be spiritual. It is carefully constructed, however, and beautifully executed. And, certainly, just because it is negative doesn't mean it is necessarily wrong. Certain aspects of the arguments about physical beauty and bodily pleasure would be refuted by many readers, and, since Boethius doesn't consider them to be all that important, are not as carefully addressed as the desires for fame or power. His overall argument, however, is carefully balanced on the inadequacy of earthly desires and attainments, and its structure is sound.
The leap from the desire for true happiness to the existence of God is not as abrupt as it sounds. It is carefully built up throughout Book III, and lays carefully on the refutation of each kind of happiness possible, according to Boethius, on earth. An atheist, animist, or other spiritual type of happiness is not discussed here - the existence of God is not really in question, it is rather the logical conclusion between two speakers who already agree that God exists. The focus is on the logical argument about the folly of earthly desires.