| Theory | Claim | Weakness |
|---|---|---|
| Consent | States are bound because they agreed | New states never agreed to existing custom |
| Custom | Binding practice creates obligation | Practice may be convenient rather than obligatory |
| Natural law | Certain principles bind regardless of consent | The content of the principles is contested |
| Necessity of the system | States need predictable rules to coexist | Explains why law exists, not which rules bind |
The practical compromise is that consent explains most obligations, while peremptory norms (jus cogens) explain the ones that cannot be escaped.