Principles Of Public International Law

How To Actually Work With Public International Law

Most people approach this subject wrong. They start by memorizing treaties and trying to recite Articles of the UN Charter like they're quoting scripture. That doesn't help you when you're sitting in a room and someone asks whether a particular state action violates customary international law. The real skill is knowing how to find the source, check whether it's binding on the party in question, and figure out whether an exception applies. I learned that the hard way. Let me cut to the core first because the textbooks bury it. Public international law isn't a single code. It's three overlapping sources listed in Article 38(1) of the ICJ Statute: treaties, customary international law, and general principles of law. That's it for the main sources. Everything else—judicial decisions, scholarly writings—is subsidiary means of interpretation, not binding authority on its own. When someone tells you "customary international law requires X," your first question should always be: which specific norm? Is it jus cogens? Is it merely erga omnes? Is it really customary or just a political declaration most states made because it's convenient? I remember dealing with a case involving a regional maritime dispute where the opposing counsel cited a 2018 UN General Assembly resolution as if it established a binding rule on exclusive economic zone delimitation. It didn't. The resolution was persuasive at best and didn't reflect consistent state practice accompanied by opinio juris. I spent about forty minutes pulling together the actual ICJ jurisprudence—North Sea Continental Shelf, Libya v. Malta—to show the court that the customary rule required equitable principles based on geography, not the position the other side wanted. The resolution was cited in passing in a few subsequent cases but never as dispositive authority. That distinction matters a lot.

Here's what most people miss about customary international law. It's not formed by what states say they believe. It's formed by what states actually do, repeatedly, over time, with the belief that they are legally obligated to do so. That second element—opinio juris—is the part that makes it exhausting to prove or rebut. State practice alone isn't enough. I've seen well-paid consultants build entire memoranda on state practice while completely ignoring the absence of opinio juris. The ICJ will tear that apart. You have to show that the state performed the act because it believed it was legally required, not for political, economic, or humanitarian reasons. On the flip side, rebutting custom is often faster if you know how. Persistent objector doctrine still exists. If a state consistently objected to a emerging norm during its formation period, it may not be bound. The classic problem is timing—objections made after the norm crystallizes don't count. I worked on a matter where our client was trying to avoid being bound by what the other side claimed was a customary prohibition on certain naval maneuvers. We found that our client had issued formal diplomatic protests on three separate occasions during the formative period in the 1990s. That was enough to carve out an exception. The other side's argument collapsed because they couldn't establish uniform state practice at that stage.

Treaty Interpretation Is Where Most People Screw Up

Vietnam is not the only country with this problem, but it's a frequent one. States ratify treaties, then interpret them in ways that benefit them, then claim those interpretations are the authoritative ones. The Vienna Convention on the Law of Treaties Articles 31 and 32 govern how you read treaties, and they're deceptively straightforward until you apply them. Article 31 says you interpret in good faith according to the ordinary meaning of the terms in their context and in light of the treaty's object and purpose. That's the primary rule. Article 32 allows supplementary means—travaux préparatoires, preparatory work—if the primary interpretation leaves the meaning ambiguous or leads to a manifestly absurd result. Most practitioners lean too hard on one or the other. You start with Article 31. You don't jump to preparatory work unless Article 31 fails you. I see this mistake constantly in briefs. Another thing that trips people up is the relationship between treaties and customary law when they overlap. A treaty provision can codify existing custom, crystallize emerging custom, or simply create a contractual obligation that exists alongside custom. The Corfu Channel case is the standard example—Albania's duty to warn of mines existed under customary law regardless of any treaty obligation. Knowing which category you're dealing with changes everything about what evidence you need to produce and what defenses are available.

Jus Cogens And Non-Derogable Norms

This category is smaller than people think and bigger than most opponents want to admit. Jus cogens norms are peremptory—no treaty, no consent, no exception. Genocide, slavery, torture, aggressive war, apartheid. That's roughly the consensus list. The problem is identifying the boundary. Not everyone agrees on every item. The prohibition on piracy is widely treated as jus cogens. The prohibition on mercenarism less so. When you're arguing a case, you need to be precise about which norm you're invoking and whether the tribunal or court you're before actually accepts it as peremptory. I handled a matter where we were dealing with extradition and the requested state invoked the torture prohibition. The requesting state argued the concern was speculative. We had to demonstrate not just that torture was prohibited—which is trivial—but that the specific risk met the threshold for non-refoulement under customary law as interpreted by the relevant bodies. The evidence turned on country conditions reports, past instances, and the structural nature of the problem in the requesting state. It took about three weeks of research and four drafted submissions. The requesting state settled before the final hearing. That's the reality of how these cases actually resolve.

State Responsibility Is The Engine Room

The Articles on State Responsibility adopted by the ILC in 2001 are the closest thing public international law has to a systematic framework for attributing conduct to states and determining consequences. They're not a treaty. They're widely regarded as reflective of customary law, which means they carry substantial weight even though no single state is bound by them solely by virtue of adoption. The ICJ treats them as authoritative restatements. National courts cite them frequently. Everyone uses them. The key provisions you need to actually work with are attribution (Article 4 through Article 11), breach (Article 12), circumstances precluding wrongfulness (Articles 20 through 25), and reparation (Articles 31 through 37). Most disputes turn on attribution. Did the conduct belong to the state? Was it a state organ? Was it exercised under the state's direction or control? The Nicaragua standard of "effective control" for private actors versus the looser "overall control" test from Tadić still causes confusion in practice. I've seen courts and tribunals pick whichever standard suited their outcome. That's not ideal but it's the current state of play. Circumstances precluding wrongfulness are another area where theory and practice diverge. Self-defense, force majeure, distress, necessity, countermeasures. Each has strict conditions. Necessity under Article 25 is particularly narrow—the act must be the only way to safeguard an essential interest against a grave and imminent peril, and the state must not have contributed to the situation. I argued necessity once for a state facing an environmental emergency caused partly by external actors. The tribunal rejected it because we couldn't establish that the measures taken were the only ones available. The state had alternatives that were politically unpopular but technically feasible. That distinction between politically difficult and genuinely impossible is the line that separates valid necessity from excuse.

Who Can Enforce These Principles And How

The ICJ handles disputes between states. The ICC prosecutes individuals for genocide, crimes against humanity, war crimes, and aggression. The ITLOS deals with maritime disputes. Regional human rights courts handle their own clusters. There's no central enforcement mechanism. Compliance depends on politics, reciprocity, reputation, and sometimes economic pressure. That's not a flaw in the system—it's the system. Understanding that changes how you approach every question. When I consult on matters involving enforcement, I start by mapping the available forums and the jurisdictional hooks each one offers. Jurisdiction in international law is consensual. You need a treaty clause, a special agreement, a declaration under Article 36(2) of the ICJ Statute, or some other basis. If your client doesn't have jurisdiction, nothing else matters. I've seen this oversight cost clients six to eight months of their time and tens of thousands in legal fees before we caught it. The workaround is always the same: identify every possible jurisdictional avenue early, rank them by likelihood and speed, and pursue the strongest one first while keeping backups ready.

What This Approach Doesn't Solve

Understanding the structure of public international law won't help you win cases where the opposing party controls the tribunal or where political considerations override legal ones. It won't help when evidence is destroyed or withheld. It won't help when customary norms are disputed and the court split is 2-1 against you. The framework gives you tools. It doesn't guarantee outcomes. Anyone telling you otherwise is selling something. The practical takeaway is that you spend about eighty percent of your time on sources and attribution and twenty percent on substantive rules. Find the source. Prove it binds your opponent. Show how it applies. Then repeat for the counterargument. That's the workflow. It's tedious. It's also the only way this system functions.