Atala Riffo and Daughters v Chile - a judgment of the Inter-American Court of Human Rights

You cannot use the case without the machinery, so state it first.

The Organization of American States was created when the Ninth International Conference of American States adopted the OAS Charter, transforming the Pan-American Union. The Charter contained two provisions on human rights: it proclaimed the fundamental rights of the individual without distinction as to race, nationality, creed or sex, and it declared that each State shall respect the rights of the individual and the principles of universal morality in developing freely its cultural, political and economic life. The same Conference adopted the American Declaration of the Rights and Duties of Man, which remains the system's basic human rights document.

The system has two organs:

• The Inter-American Commission on Human Rights, established by the OAS in 1959. It applies throughout the 35 member States of the OAS.
• The Inter-American Court of Human Rights. Under Chapter VIII of the American Convention the Court consists of seven judges of the highest moral authority, drawn from the member States of the Organization, elected to six-year terms by the OAS General Assembly and eligible for re-election for one further six-year term. No member State may have more than one judge on the Court at a time; where a State is a defendant and has no judge of its nationality sitting, it may appoint a judge ad hoc for the case. The Court began operating in 1979 and soon issued several advisory opinions.

The number that matters for a comparative answer: of the 35 OAS member States, 23 have ratified the American Convention, and of those, 20 have accepted the Court's contentious jurisdiction. So the American system has two thresholds where Europe has none - ratification of the Convention, and a separate acceptance of contentious jurisdiction - and that is why a comparative answer should say that access to the American Court is narrower than access to the European Court even though the rights protected are similar.

The Chilean Supreme Court awarded custody of a mother's children to their father because of the mother's sexual orientation. She was a lesbian, and that fact was treated by the national court as material to her fitness as a parent.

The Inter-American Court upheld the mother's right to hold custody of her child under the Convention. It held that laws which discriminate on the basis of sexual orientation are prohibited, and that sexual orientation is an improper classification.

Following the judgment, the Chilean Supreme Court nullified the laws which discriminated against LGBT persons.

That is what a working regional system looks like, and it is why the case is worth more to you than its facts. The sequence runs: national court decides against the individual; regional court finds the national decision incompatible with the Convention; the national legal order changes. A regional human rights court has no police and no prison. Its output is a judgment. Whether the system works is a question about whether that judgment produces domestic change, and here it did.

The technique will be familiar from Indian equality jurisprudence and the comparison is worth drawing.

A classification is a rule that treats one group differently from another. Every legal system permits classification; what it forbids is classification on grounds that have nothing to do with the objective pursued. The objective in a custody case is the welfare of the child. The mother's sexual orientation has no rational bearing on that objective; treating it as decisive is therefore not a classification at all but a prejudice with a legal form.

Compare Article 2 of the Universal Declaration, which entitles everyone to the rights and freedoms set out in it "without distinction of any kind, such as race, colour, sex, language, religion, political or other opinion, national or social origin, property, birth or other status". The words other status are the hook. Sexual orientation is not named in the Declaration, in the Covenants, or in the American Convention, because none of them was drafted with it in mind. The open-ended residual category is how the instruments of 1948 and 1966 remain capable of application to a question their drafters did not ask.

That is a general lesson about the interpretation of human rights instruments and it is worth saying in an essay: these are living instruments, and the residual clauses are the mechanism by which they live.