The doctrine of natural law is one of the most popular legal doctrines. This doctrine was initiated by several leading legal experts, starting from Hugo Grotius to Mochtar Kusumaatmadja.

This doctrine has also been adopted in several legal systems. Until now, this doctrine is still one of the studies in law.

Natural Law Doctrine of the Greco-Roman Era

In philosophy before Aristotle, law nature is the rule of the universe, and at the same time the rule of living together through laws. In the philosophy of the Sophists, natural law is interpreted as "the law of the strongest", which cannot actually be called law; what is called natural law here is nothing but power and violence.

Aristotle was the first to distinguish between natural law and positive law. According to him, natural law is a law that always applies everywhere because of its relationship with the laws of nature. This law never changes, never disappears and applies by itself. This natural law is distinguished from positive law, which entirely depends on human provisions.

For the Sophists, nature is something external, something outside of humans. Meanwhile, Aristotle, in his book "logic" views the world as a totality that encompasses all of nature. Humans are part of nature, endowed with an active mind that distinguishes them from all other parts of nature. Humans are only able to form their will according to their rational understanding. This thesis of Aristotle becomes the basis of the conception of law nature of the Stoic philosophers.

The school of philosophy that most influenced the Roman view of law was the Stoic school. The basic idea of Stoicism is that everything that exists is an orderly unity (cosmos), thanks to a principle that guarantees that unity, namely the soul of the world (logos). Logos is none other than the Divine Mind, which animates everything.

This school of thought argues that human co-existence has a relationship with logos, namely through universal law (lex universalis) which is found in everything. This universal law is contained in the logos, and as such is called eternal law (lex aeterna). As far as eternal law becomes manifest in the universe, it is called natural law (lex naturalis). This natural law is independent of people, always applies and cannot be changed. This natural law is the basis of all positive law.

The Stoic philosophers distinguished between relative and absolute ideals of natural law. During the heyday of natural law, there were no families, slavery, property rights, or government. But these institutions became important with the decline of human morality. "Relative" natural law requires legislators to have laws that are guided by reason, and as close as possible to absolute natural law.