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.