This article seeks to justify the claim that Thomas Aquinas proposed a concept of natural law which is immune to the argument against the recognition of an objective grounding of the good formulated by a well-known representative of the liberal tradition, Isaiah Berlin, in his famous essay “Two Concepts of Freedom.” I argue that Aquinas’s concept of freedom takes into account the very same values and goals that Berlin set out to defend when he composed his critique of natural law. In particular, the article suggests that Aquinas recognizes freedom as a greater perfection of man than rationality, and that this freedom is realized, among other things, through the co-construction of the good that gives a goal and a shape to human action and to the whole of a person’s life. I argue that the co-construction of such a good involves the co-construction of natural law in the strict sense of the term. Indeed, the content of natural law can be understood as a set of goods which are goals that inform human action. From a human perspective, natural law is not a pre-existing recipe which has merely to be “read.” Defining the concrete content of natural law is an ongoing process. The process of defining natural law’s content takes humanly knowable, objective elements into account, and so draws on knowledge. Yet free choice also plays an important part in this process. When speaking of the process of defining the content of natural law, therefore, and in determining what here-and-now is to be done, it is reasonable to describe man as a creator of the natural law, or as a legislator, just as the members of a parliament are the creators of civil law — bearing in mind that only a just law is truly law and therefore the creation of both civil and natural law reaches only as far is the scope of just actions directed by these laws. From the perspective of human action, we may speak of each person’s free choice to establish a given good as the end of a specific act, and in so doing to declare that action proper under natural law in the strict sense of the term (which differs from the rules of natural law).
An appreciation of what is particular and individual (particulare et individuum), and an appreciation of free choice that goes hand-in-hand with this, is deeply embedded in Thomas’s system of thought. Particularity and individuality has its basis in an especially excellent way of human existence.