Citizenship is a republican concept. A citizen is someone who is equal before the law, that is, the law applies equally to everyone. Historically, this was not always the case - even in classical times (Greece’s city-states and the Roman Republic) from where we get the modern term “citizen”. By way of contrast, a “subject” is someone who is subject of a monarch. As Charles I, the King of England and Scotland who was overthrown by his own parliament, said:

A Sovereign and a Subject are clean different things

In 1948, the British Nationality and New Zealand Citizenship Act was passed. The Hansard record of the debate on the Act is instructive:

The word “subject” implies Government ownership. The word “citizen” means means that within the range of the prudently possible, the invidual is co-ordinate, not sub-ordinate.

Why did New Zealanders become “citizens” and not “subjects”? Why weren’t New Zealanders titled “New Zealand Subjects”?

The creation of New Zealand citizenship, like most of our moves towards independence, was forced on us by events elsewhere. Canada went ahead in 1947 and created its own citizenship, the Irish Free State in transforming itself into the Republic of Ireland created its own Irish citizenship as well. The independence of India and Pakistan also in 1947 saw those new countries create their own citizenship rules. The term “British subject” was rapidly being replaced.

So once again the term New Zealand used was decided for us elsewhere. Despite an attempt by the House of Lords to amend the UK’s equivalent legislation to replace “Commonwealth citizen” with “Commonwealth subject”, citizenship became the order of the day.