Explanation : The principle of equity includes both horizontal and vertical. Equity is determined by first assessing an individual's ability-to-pay. The idea of the ability-to-pay principle considers whether or not it is fair to tax someone higher just because that person has the ability and resources to pay. If it is decided that they should be required to pay more, the question of how much more arises. These questions can be analyzed through horizontal and vertical equity which are subsets of the ability-to-pay principle. Horizontal equity suggests it is fair for people of equal ability to pay the same amount in taxes. Vertical equity is the idea that people who has a higher ability to pay more than those who have a lower ability to pay, as long as the increase in tax level is considered to be reasonable. ....Read more