The definition of Natural Law from the Oxford Companion to Philosophy:
Moral standards which, on a long-dominant but now disfavoured type of account of morality, political philosophy, and law, can justify and guide political authority, make legal rules rationally binding, and shape concept – formation in even descriptive social theory.
The sounder versions (e.g. of Plato, Aristotle, and Aquinas) consider morality ‘natural’ precisely because reasonable ( in an understanding neither consequentialist nor Kantian). Likewise, contemporary versions plead not guilty of the ‘is – ought’ fallacy: natural law’s first ( not yet specifically) principles identify basic reasons for action, basic human goods which are – to – be (ought to be)instantiated through choice.
Practical knowledge of these presupposes, but is not deduced from, an ‘is’ knowledge of possibilities; full ‘is’ knowledge of human nature is partly dependent on, not premiss for, practical (’is-to-be’) understanding of the flourishing (including moral reasonableness) of human individuals and communities.
