International law rests on a seemingly intuitive foundation: states are bound only by rules they have accepted. Treaties require ratification. Custom requires state practice. The entire edifice appears to derive its authority from the voluntary agreement of sovereign nations. This voluntarist picture dominates both legal doctrine and political common sense.

Yet this foundation contains a fatal flaw. The moment we ask why consent creates binding obligations, we discover that consent alone cannot answer the question. Something must explain why promises bind—and that something cannot itself be a matter of consent without triggering an infinite regress. The voluntarist account, upon examination, presupposes the very normative framework it claims to generate.

This matters beyond academic theory. If international law's authority derives solely from state consent, then powerful states can exempt themselves from inconvenient obligations simply by withdrawing consent. If certain obligations bind regardless of consent, we need to understand why—and what this implies for how we think about global order. The stakes involve everything from human rights enforcement to climate agreements to the basic question of whether international law is law at all or merely institutionalized bargaining between self-interested sovereigns.

Voluntarists hold that international legal obligations arise from state consent—whether through explicit treaty acceptance or implicit acquiescence to customary norms. This position appeals to sovereignty: no state can be bound by rules it has not chosen. Yet the very mechanism of consent presupposes norms that consent cannot generate.

Consider the basic logic. For consent to create binding obligations, there must already exist a norm that consent binds. Call this the pacta sunt servanda principle—agreements must be kept. But where does this prior norm come from? If it too derives from consent, we face an infinite regress: we need consent to establish the norm that consent binds, which requires a prior norm that that consent binds, and so on indefinitely.

The voluntarist might appeal to the Vienna Convention on the Law of Treaties, which codifies pacta sunt servanda. But this merely relocates the problem. The Convention itself is a treaty—why does it bind? Because states consented to it? Then we need an explanation of why that consent creates obligations, which cannot itself rest on the Convention without circularity.

Some theorists attempt to ground the binding force of consent in the nature of promising itself. To make a promise while intending not to keep it involves a kind of performative contradiction. But this move abandons pure voluntarism—it appeals to moral or logical facts about promising that exist independently of what states have agreed to. The binding force of consent becomes derivative of deeper normative truths.

The paradox reveals that voluntarism cannot be the whole story. Even if we preserve a significant role for consent in international law, we must acknowledge that consent operates against a background of non-consensual normative foundations. The question then becomes what those foundations are and what they imply for obligations that states claim they never accepted.

Takeaway

Consent can create obligations only because something deeper than consent makes promises binding. The foundation cannot be self-supporting.

International law itself recognizes obligations that override state consent. Jus cogens norms—peremptory norms of general international law—bind all states regardless of agreement and cannot be modified by treaty. Genocide, slavery, torture, and aggressive war are prohibited absolutely, not conditionally on state acceptance.

The Vienna Convention on the Law of Treaties declares that any treaty conflicting with a jus cogens norm is void. This is remarkable: states can consent as enthusiastically as they like to a treaty permitting genocide, and it has no legal force whatsoever. Consent is not merely insufficient; it is entirely irrelevant to whether the prohibition binds.

Voluntarists struggle to explain jus cogens within their framework. Some argue that these norms reflect universal state consent—every state has accepted them. But this is empirically questionable and misses the doctrinal point. The norms bind because of their content, not because of acceptance. A newly formed state is bound by jus cogens the moment it exists, without any opportunity to consent or dissent.

The existence of peremptory norms suggests that international law recognizes a category of obligations grounded in something other than consent. The most plausible candidate is moral necessity: some acts are so fundamentally wrongful that no legal system worthy of the name can permit them. This introduces natural law considerations that pure positivism—the view that law derives entirely from social facts like consent—cannot accommodate.

If moral principles ground some international obligations, we must ask whether they might ground others. Perhaps the prohibition on torture is merely the most obvious case of a broader phenomenon: international law drawing legitimacy from sources beyond state agreement. The existence of jus cogens opens a door that cannot easily be closed.

Takeaway

International law already recognizes that some obligations bind regardless of consent. The question is not whether non-consensual obligations exist, but how far they extend.

If consent cannot fully ground international law, what can? Three alternatives deserve attention: moral principles, functional necessity, and legitimate expectations. Each captures something important about why international legal obligations bind.

The moral principles approach holds that certain international obligations derive from universal moral truths—human rights, duties of mutual aid, prohibitions on harm. States are bound because the underlying moral requirements are genuine, regardless of what states have agreed. This explains jus cogens straightforwardly and suggests that other morally grounded obligations might bind similarly. The challenge is specifying which moral principles generate legal obligations and how to adjudicate disagreements about moral content.

The functional necessity approach focuses on coordination problems that require international solutions. Climate change, pandemic disease, financial contagion—these challenges cannot be addressed by individual states acting alone. International law gains authority from its necessity for achieving goods that states cannot secure independently. Obligations bind because the alternative—an uncoordinated world—is catastrophically worse for everyone. This grounds law in prudential rather than moral necessity, though the two may converge.

The legitimate expectations approach emphasizes reliance and trust. When states participate in international legal systems, they create expectations in other states and in individuals. Withdrawing from obligations damages those who relied on compliance. This generates obligations through the wrong of betraying justified reliance rather than through the inherent bindingness of consent. Expectations can be legitimate even absent formal consent, grounding obligations in relationships rather than agreements.

None of these alternatives eliminates consent entirely. Consent remains significant for specifying the content of obligations and for generating legitimacy through participation. But consent operates within a framework of prior normative constraints—moral limits, functional requirements, relational duties—that shape what consent can accomplish and what obligations exist independently of it.

Takeaway

International law's authority likely rests on multiple foundations: moral principles that constrain, functional needs that compel, and legitimate expectations that bind through relationship rather than agreement.

The voluntarist picture of international law—sovereignty preserved through consent-based obligation—cannot survive philosophical scrutiny. Consent presupposes the very normative foundations it purports to create. International law's own doctrine of peremptory norms acknowledges obligations that override agreement. The question is not whether non-consensual foundations exist, but how to theorize them adequately.

This has profound implications for global governance. If international law binds through moral principles and functional necessity, not merely state agreement, then powerful states cannot legitimately exempt themselves from inconvenient obligations. Withdrawal from climate agreements or human rights frameworks does not eliminate the underlying duties—it merely violates them.

Understanding international law's true foundations is essential for confronting global challenges that require coordinated action regardless of whether every state enthusiastically consents. The work of global political theory is to articulate frameworks adequate to this reality.