[This is part of the series: The Complete Guide To Economics 101.]
What is defined as the ability-to-pay principle?
The Ability-to-Pay Principle is a principle that says that taxes should be taxed based on the ability to endure the burden.
A 70% income tax rate on incomes under the poverty line would obviously violate the ability-to-pay principle. Too much income tax, on too little income.
On the other hand, a progressive income tax rate, where higher taxes are paid on higher and higher amounts of income would follow the ability-to-pay principle.