Taxation equity may be classified into horizontal equity, where people who are in the same economic position should be taxed the same, and vertical equity, where those who differ economically should be treated differently. In the New Zealand income tax, the vertical equity norm has primarily been achieved by progressive tax rates, and by family-friendly adjustments. Given that the income tax intentionally discriminates between taxpayers on the basis of taxpayer-specific characteristics such as income level and domestic situation, the question arises as to how the New Zealand income tax in its successive manifestations has been justified as fair; that is, what vertical equity in the New Zealand income tax looked like and how it was justified...