"The Origin of the Idea of Natural Right," Social Research, Vol. 19, No. 1 (March 1952).  Reprinted in Natural Right and History (Ch. 3).

Excerpt:

To understand the problem of natural right, one must start not from a “scientific” understanding of political things but from a “natural” understanding of them, that is, from the way in which they present themselves in political life – in action, when they are our business, when we have to make decisions. This does not mean that political life necessarily knows of natural right. Natural right had to be discovered, and there was political life prior to that discovery. It merely means that political life in all its forms necessarily points toward natural right as an inevitable problem. Awareness of this problem is not older than political science, but coeval with it. Hence a political life that does not know of the idea of natural right is necessarily unaware of the possibility of political science, and indeed of the possibility of science as such, just as a political life that is aware of the possibility of science necessarily knows natural right as a problem.

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