Generally accepted principles of international law are those legal principles which are so basic and fundamental that they are found universally in the legal systems of the world.

Article 38 of the Statute of the International Court of Justice sets out the following sources of international law: (1) international conventions, whether general or particular, establishing rules expressly recognized by the contesting states; (2) international custom, as evidence of a general practice accepted as law; (3) general principles of law recognized by civilized nations; and (4) judicial decisions and the teachings of the most highly qualified publicists of the various nations as subsidiary means for the determination of rules of law.^[32]

Essentially, conventional international law is the body of international legal principles contained in treaties or conventions as opposed to customary international law or other sources of internationaL law.^[33]

Customary international law is defined as a general and consistent practice of states followed by them from a sense of legal obligation.^[34] I had occasion to explain the concept of customary international law as used in our Constitution in this wise:

Generally accepted principles of international law, as referred to in the Constitution, include customary international law. Customary international law is one of the primary sources of international law under Article 38 of the Statute of the International Court of Justice. Customary international law consists of acts which, by repetition of States of similar international acts for a number of years, occur out of a sense of obligation, and taken by a significant number of States. It is based on custom, which is a clear and continuous habit of doing certain actions, which has grown under the aegis of the conviction that these actions are, according to international law, obligatory or right. Thus, customary international law requires the concurrence of two elements:

[1] the established, wide-spread, and consistent practice on the part of the States; and

[2] a psychological element known as opinio juris sive necessitatis (opinion as to law or necessity). Implicit in the latter element is a belief that the practice in question is rendered obligatory by the existence of a rule of law requiring it.^[35]

In the North Sea Continental Shelf Cases,^[36] the International Court of Justice held that "[n]ot only must the acts concerned amount to a settled practice, but they must also be such, or be carried out in such a way, as to be evidence of a belief that this practice is rendered obligatory by existence of a rule of law requiring it. The need for such a belief, i.e., the existence of a subjective element is implicit in the very notion of the opinio juris sive necessitatis."

Moreover, to be considered as customary international law, a rule must apply to all, or majority of all, states. One possible exception to the universal applicability of customary international law is local or special custom. A local or special customary international rule binds only a group of states, regional or otherwise.^[37] "Regional customary international law refers to customary international law that arises from state practice and opinio juris of a discrete and limited number of states; as it departs from generally applicable customary international law, it is only binding upon and opposable against those states participating in its formation."^[38]

Generally accepted principles of international law are those legal principles which are so basic and fundamental that they are found universally in the legal systems of the world. These principles apply all over the world, not only to a specific country, region or group of states. Legal principles such as laches, estoppel, good faith, equity and res judicata are examples of generally accepted principles of international law.^[39] In Pharmaceutical and Health Care Association of the Philippines v. Duque III,^[40] the Court further explained the concept of generally accepted principles of law, to wit:

Some legal scholars and judges look upon certain "general principles of law" as a primary source of international law because they have the "character of jus rationale" and are "valid through all kinds of human societies." (Judge Tanaka in his dissenting opinion in the 1966 South West Africa Case, 1966 I.C.J. 296). O'Connell holds that certain principles are part of international law because they are "basic to legal systems generally" and hence part of the jus gentium. These principles, he believes, are established by a process of reasoning based on the common identity of all legal systems. If there should be doubt or disagreement, one must look to state practice and determine whether the municipal law principle provides a just and acceptable solution. x x x