Again, when a lawless band of men, such as the mutineers of The Bounty, settle down in some uninhabited island outside the pale of civilisation, they are sometimes described as being governed by the "law of nature" – that is, surely, by the remnants of their consciences.
Common Law Of England, W.B. Odgers, Vol.1, p. 2.
…"that man should pursue his own happiness." This is the foundation of what we call ethics, or natural law. … This law of nature, being co-eval with mankind and dictated by God himself, is of course superior in obligation to any other. It is binding over all the globe, in all countries, and at all times: no human laws are of any validity, if contrary to this; and such of them as are valid derive all their force, and all their authority, mediately or immediately, from this original.
But in order to apply this to the particular exigencies of each individual, it is still necessary to have recourse to reason; whose office it is to discover, as was before observed, what the law of nature directs in every circumstance of life; by considering, what method will tend the most effectually to our own substantial happiness. And if our reason were always, as in our first ancestor before his transgression, clear and perfect, unruffled by passions, unclouded by prejudice, unimpaired by disease or intemperance, the task would be pleasant and easy; we should need no other guide but this. But every man now finds the contrary in his own experience; that his reason is corrupt, and his understanding full of ignorance and error.
Commentaries on the Laws of England Book the First, William Blackstone, 1758
Natural law is at least the mediate cause of every obligation; for if contracts and injuries produce any obligation, it is because natural law requires every person to perform his promises, and to repair the injuries which he has wrongfully occasioned.
A Treatise on the Law of Obligations or Contracts, M. Pothier, 1806. Part 1., Ch. 1., s.2.