The philosophy of natural law is that inherent to human nature is a system of standards common to all mankind. Cicero claimed it was "the safety of citizens, the preservation of states, and the tranquility and happiness of human life." Hobbes insisted it was the protection of the individual. Jefferson said, "Life, liberty, and the pursuit of happiness [personal support and fulfillment]." Paul touched on natural law regarding the knowledge of God's attributes (Romans 1:18-20) and the law written on Gentiles' hearts (Romans 2:14-15).
What does natural law teach?
Natural law is determined by the reasoned analysis of that part of human nature which is universal and not merely cultural—natural law applies to everyone, regardless of culture or era. Contemplation of that shared nature leads to the derivation of the ultimate purpose for which human nature was intended. This purpose, or telos, suggests standards which, if followed, will best result in the fulfillment of the telos and, consequently, of human nature itself. The definition of telos, unlike that of natural law, has remained fairly stable throughout history, and often reflects basic biblical standards. Respect for life (Genesis 9:5-6), procreation (Genesis 1:28), and some kind of personal fulfillment are generally included.
Once the telos of mankind is determined, natural law can be defined. Where life is valued, murder is taboo. Where procreation is valued, mores dictate that women are not allowed to commit adultery (because women need support to raise young, and the desire to procreate discourages men from raising another man's child). Where physical safety is valued, violence is discouraged. If people determine that telos and natural law are best fulfilled in the context of a society, they follow Cicero's lead in including the preservation of that society in natural law. Conversely, libertarians tend to view the telos of mankind as more individualized, and believe the application in regard to government is for it to keep the peace and stay out of the way. Either way, civil law is developed to define the responsibilities of society to fulfill natural law.
The idea of natural law gets trickier when atheistic evolution gets involved. According to atheistic evolution, mankind has no universal telos. We are nothing more than a complex system of atoms that came about randomly. But most atheistic evolutionists do not wish to completely abandon natural law. It is obviously wrong to torture innocents and cause unjust wars. The telos, then, applies not to humanity, but to the anthropomorphized drive that induces genes to replicate themselves. It is "survival of the fittest," reverse-engineered. Fit genes survive. Therefore, the environment in which they survive must be conducive to their survival. "Natural law" is one part of that environment; the genes that survive best in a peaceful environment thrive in proximity to genes that encourage peace. Genes need life to replicate, so the carriers—mankind—generally value life. An entire branch of psychology (evolutionary psychology) has been developed to explain how the replication of genes has controlled the sociology, psychology, and biology of mankind outside of the influence of a Creator. And yet atheists cannot explain such phenomena as altruism, suicide, and martyrdom. If materialism is true and we are nothing but physical stuff, and only the physical stuff that survives can procreate, then anomalies that discourage personal survival, such as martyrdom, should have been bred out generations ago.
Post-modernism has taken this argument further. Instead of relying on the metaphorical telos of genes, it claims there is no telos in the universe. There is no human nature. There is no purpose that all mankind shares. There is no purpose-giver. Therefore, there is no natural law. Furthermore, all ethics and morality are subject to being redefined by the individual and his circumstance. While the critique of accepted norms can be helpful (lest cultural norms of one era be continued as inappropriate absolutes in another), rejection of a universal telos and morality isn't conducive to a productive society. Just the fact that society can and does exist should be enough to contradict relativism.
Most cultures accept that human nature not only has a telos, but that the telos was endowed by the Creator. Theists believe telos in its most basic form is communion with God. But they don't agree that natural law necessarily follows. Within theistic circles, the counter-proposal to natural law is "divine command theory." The argument is convoluted, but goes something like this: Given, that God is good and gave mankind the telos of communion with Him. How is "good" determined? If God is sovereign to the point that He defines "good"—He commands the definition of "good"—that is divine command theory, and He spoke "good," His own divine law, and our natural law into being. But if God has the sovereignty to determine "good," then He can choose anything to be good, up to and including the torture of innocents. Torturing innocents is not good, as the careful reasoning of human nature will universally agree. Therefore, according to this reasoning, God cannot have the sovereignty to command "good." Morality is a cosmological absolute, independent of God. But that not only makes natural law independent of God, it makes God subject to morality. Yet, if God is God, He is not subject to any outside authority, so He must be the author and definer of "good"…
The answer is both/and. God is. He is the "I AM." He defines "good" because He embodies good. He created us for communion with Him. To make that possible, He created us to operate in a way that would relate to His nature. Therefore, He designed natural law to reflect and complement His nature. At the same time, He is free to command good because His commands are not arbitrary or rhetorical. They are the Logos that created the world (John 1:1). The Logos/divine-command spoke into being the way in which we would best relate to God. Logic based in truth created natural law.
An overemphasis on natural law is not necessarily helpful. In history, natural law has developed a bad habit of elevating cultural attitudes to the level of human destiny; it was in the name of natural law that different ethnicities and women were considered inferior. Even if God developed a law for mankind to live by that is discoverable by the application of human reason to human nature, we have to recognize that both our reasoning and our nature are fallen. Our fallen reason cannot accurately determine the exact God-given purpose of our fallen nature. Even if it could, it's telling that God still outlined orders—commands that we consider the backbone of natural law—to the unfallen Adam and Eve (Genesis 1:28). This should be a strong indication that whatever the discussion on natural law, God has outlined what He expects of us in His Word. We don't have to analyze or discuss; just read. In and among the intuitive commands such as "be fruitful and multiply" and the not-so-intuitive commands such as "consider trials joy" (cf. James 1:2), we find Micah 6:8: "He has told you, O man, what is good; and what does the LORD require of you but to do justice, and to love kindness, and to walk humbly with your God?"
What is Naturalism?
What does moral absolutism say about ethics and morality?
What does moral relativism say about ethics and morality?
What does ethical relativism say about ethics and morality?
How does cultural relativism influence society?
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