NEW DELHI, June 24 -- A passport can get an Indian across international borders, secure consular protection in a foreign country and establish nationality before immigration authorities worldwide. Yet, according to officials of the external affairs ministry, it is not proof of citizenship.

The seemingly technical clarification, made on Passport Seva Divas on Wednesday while unveiling the benefits of chip-enabled e-passports, has revived a long-standing legal question that has acquired renewed significance amid recent controversies over electoral roll revisions and citizenship verification exercises: if even a passport does not conclusively prove citizenship, what document does?

The paradox

The statement appears counter-intuitive becaus...