(continuing the series on sources of international law)
One source of international law that is so basic it’s easily overlooked is that of general principles of law. This refers to the rules and principles that exist in most legal systems. They have such a fundamental nature that they are recognized as principles of international law as well.
A great example of this type of legal principle is pacta sunt servanda — that promises given must be kept. This basic natural law concept is part of the core of legal relationships. Similarly, other international laws stem from such basic legal logic concepts and arguments that they are difficult to disagree with.
Another example of a general principle of natural law leading to a corollary rule of international law is that of restitution. Natural law has long required that one who harms or wrongs another must make restitution for the harm done.
In many respects, the arguments in support of international laws based on general legal principles have an equitable character. This can often be an obstacle, as some judges are hesitant to rely on arguments based in equity, because of the politics that often surround them. It can tend to give the appearance of creating law as opposed to interpreting it. Additionally, relying on general principles of law and equity can tend to leave gaps in the legal development, such that it makes the result of a dispute unpredictable.
However, even old general principles of law provide for considerations of equity when deciding a case. This stems from the sometimes relied upon principle of ex aequo et bono — which provides for doing what is fair.