Historically, there are two main approaches to international law:
– Natural law, which can be thought of as the idea that power of law does not come from voice of authority. In contrast positivisim says the authority is what makes the law the law. Natural law says there is a higher reason why the law is the law (e.g morality, universal principles, religious, etc.). Under natural law, horrific immoral laws would not be valid even if they came from a legitimate authority.
The application of these approaches goes back 2000 years. Natural law finds its origins in ancient Rome and Cicero the philosopher. Thomas Aquinas examined source of the aw’s legitimacy; according to him natural law is God’s natural law.
A modern definition explores how natural law is universally applicable with rules derived from reason; a doctrine that human affairs should be governed by ethical principles understood by reason.
Other notable contributors to the historical development of ‘natural law’ include Hugo Grotius – philosopher from Dutch Republic, who is often regarded as the father of international law. His view was that source of international law is oriented towards natural law. He argued that even if we reject theological basis of natural law, the ideas are sufficiently evident from reason to allow us to follow them. In the formation of natural law in the early years, states were not exclusive subject of international law and non state actors were able to participate. The later positivist doctrine removed the rights and obligations of individuals from international law.
In the early 20th century positivism grew and naturalist law shrunk.
– Contributions from Jeremy Bentham, 1800s and the principles of moral and legislation. His work ushers in end to natural law. He defined international law as concerned transactions between sovereigns and divided international law into two categories: public and private, the former referring to states and the latter to individuals.
We can describe positivism in general as: paradigm holds international law based on state consent. This would be created in contractual like fashion between states. For many years a related idea was popular: that only states are subjects of international law. After WWII, individuals were decided to have rights and obligations under international law (e.g. Nuremberg trials, crimes against humanity, genocide, etc.).
There are 3 key assumptions of positivism as explanation for law’s legitimacy: positive declaration i.e. law must be expressed; IL is created by sovereign states which are the subject of international law; it holds that law is effective even if it is unjust when measured against some moral standard ie there is no necessary conformity of international law to morality.
Some additional thoughts to consider:
-jus cogens. A peremptory norm. Is a fundamental principle of international law which is accepted by the international community of states as a norm from which no derogation is ever permitted.
-how can jus cogens exist in the context of positivism. States are bound by jus cogens norms, but positivism suggests laws can only exist pursuant to some sort of authoritative body. There is an apparent disconnect.
– Establishment of UN a new era of multilateral law making began.
Natural law would understand international law as the source being a validity that comes from a system of norms such as reason or morality. A natural law understanding would say that a law cannot be created by states that contravenes jus cogens norms.
A positivist approach would say that its state consent that creates international law. Law does not have to be consistent with morality or a higher state of reason.