To demonstrate the idea or feeling or concern behind natural law, and the approach that philosophers of natural law bring to the discussion, I reproduce here an extended quote from Frederick Copleston’s A History of Philosophy, volume 1: Greece and Rome-from the Pres-Socratics to Plotinus. This post also goes a good way in answering a question a friend of mine asked me recently on the justifications we have in calling some things right and others wrong, and what the foundations might be.
While we cannot accept the over-intellectualist attitude of Socrates, and agree with Aristotle that ἀκρασία or moral weakness is a fact which Socrates tended to overlook, we willingly pay tribute to the ethic of Socrates. For a rational ethic must be founded on human nature and the good of human nature as such. Thus when Hippias allowed unwritten laws, but excepted from their number laws which varied from State to State, remarking that the prohibition of sexual intercourse between parents and children is not a universal prohibition, Socrates rightly answered that racial inferiority which results from such intercourse justifies the prohibition. This is tantamount to appealing to what we would call “Natural Law,” which is an expression of man’s nature and conduces to its harmonious development. Such an ethic is indeed insufficient, since the Natural Law cannot acquire a morally binding force, obligatory in conscience–at least in the sense of our modern conception of “Duty”–unless it has a metaphysical basis and is grounded in a transcendental Source, God, Whose Will for man is expressed in the Natural Law; but, although insufficient, it enshrines a most important and valuable truth which is essential to the development of a rational moral philosophy. “Duties” are not simply senseless or arbitrary commands or prohibitions, but are to be seen in relation to human nature as such: the Moral Law expresses man’s true good. Greek ethics were predominantly eudaemonological in character (cf. Aristotle’s ethical system), and though, we believe, they need to be completed by Theism, and seen against the background of Theism, in order to attain their true development, they remain, even in their incomplete state, a perennial glory of Greek philosophy. Human nature is constant and so ethical values are constant, and it is Socrates’ undying fame that he realised the constancy of these values and sought to fix them in universal definitions which could be taken as a guide and norm in human conduct. [pages 110-11]