Summa Theologica

Following earlier thinkers like Aristotle and Boethius, Aquinas analyzes various human goals to show that they do not constitute happiness, or the greatest good.

1.  We can see that the greatest good does not consist in wealth and material possessions: The more we possess them the more we see that they are insufficient, because we always want more of them. In contrast, the more we possess the greatest good the more we love it and are satisfied in it.

2.  Happiness does not consist in honor, because honor is a sign of an excellence already existing in the person.

3.  Happiness does not consist in human glory or fame, because these things are instable and sometimes deceptive or based on false knowledge.

4.  Happiness does not consist in power: because power is a principle rather than a last end, and because power has relation to both good and evil.

Moreover, happiness consists of none of these things because each of them are in some way compatible with evil use. The supreme good must be incompatible with evil.

No bodily good can constitute man’s happiness, because the body is only part of man’s being. Man consists of body and soul, and the latter is the higher principle.

Pleasure and delight are not happiness, but merely an accidental result of happiness.

Happiness does not consist even in goods of the soul, since the soul cannot be its own last end; the last end is something outside the soul, and this is God. Thus, all lesser goods—classified as external goods, goods of the body, and goods of the soul—are desired for the sake of the greatest and universal good, which is God. Happiness is that beyond which nothing else is desired. 

Insofar as it is a quality existing in man, happiness is something created. God alone has happiness in his very self, lacking nothing; man is happy only by participation. Happiness is called man’s supreme good because it consists in the attainment or enjoyment of the supreme good which is God.

Man’s ultimate happiness consists in the Beatific Vision—the sight of God in his Essence. 

Happiness is a perfection of the creature, and admits of various degrees of perfection. Perfect happiness is not attainable in this life. Nevertheless, we can participate in happiness to some degree now. For example, the contemplative life is closer to happiness than the active life. Happiness is an act of the intellect delighting in truth.

In this life, we advance from a perfection of the lower part of our nature (e.g., the senses) to a perfection of the higher part (e.g., the intellect). In the afterlife it will be the opposite: The perfections of our higher nature will flow down to our lower nature, so that our senses and body will be receive greater perfection than they had in this life. 

Now Aquinas delves into specific things that contribute to happiness.

Three things come together in happiness:

1.  vision (knowledge of the final end, i.e., God)

2.  comprehension (presence of the end)

3.  delight (enjoyment or repose in the thing loved)

A good will is a necessary precondition for attaining happiness. The soul can be happy while separated from the body; yet in this life a well-disposed body and external goods are a necessary requirement for exercising virtue, which contributes to happiness. Friendship is not absolutely essential to final happiness, but it conduces to the well-being of happiness. 

All human beings desire happiness, although many do not know what constitutes happiness. Happiness is within man’s grasp, since the desire for it is naturally implanted in him. God rewards good works with happiness in heaven, and there are degrees of happiness according to one’s individual merits. While humans can attain a certain participation of happiness in this life, perfect happiness remains in the next life. Once attained, this happiness can never be lost.