According to St. Thomas Aquinas, philosophy is the work of reason seeking to understand the order of things. Wisdom, he explains, is the perfection of our faculty of reason, and the task of the wise man is to set things in order. While our senses can know individual material things, only reason is able to understand how things relate to one another and how they are directed to their proper ends or purposes.
There are two main kinds of order that reason considers. The first is the order of parts within a whole—for example, how the different parts of a building fit together. The second, and more important, is the order of things to their final end or purpose—like how all the parts of an army are ordered by a general to win a battle. This second kind of order gives meaning and purpose to the first.
St. Thomas explains that the wise man seeks to understand these kinds of order in four ways:
First, the wise man seeks to know the order that exists in the natural world—the order established by God in creation. This is pursued through the study of Natural Philosophy, which includes the study of physical things (Physics) and of existence itself, which is called Metaphysics.
Second, the wise man seeks to know the order that ought to exist within his soul, especially in his thoughts and in the words that express them. This is pursued through the study of Rational Philosophy, also called Logic.
Third, the wise man seeks to know the order that ought to exist in his will, so that he may live as a good man. This is pursued through the study of Moral Philosophy, or Ethics.
Fourth, the wisdom gained through philosophy enables the wise man to produce order outside himself—in the things he makes and does. This belongs to the Mechanical Arts, in which reason brings order to external things.
From these four areas of inquiry arise the principal branches of classical philosophy. Natural Philosophy studies the order of things that reason observes in the natural world. Rational Philosophy studies the order that reason produces in thought. Moral Philosophy studies the order of human choices and actions. And the Mechanical Arts apply reason to shape and arrange the physical things man controls.
This, according to St. Thomas, is what philosophy truly is: the habit of reason studying the different kinds of order found in the world, in thought, in action, and in human works. Above all, it is Moral Philosophy that studies how human life itself is to be ordered—one action to another, and all things to our highest end, which is eternal happiness. This is what we study in classical philosophy.
