Yes, they must depend on what you earn.. How can you ask a citizen earning 10 to pay 5 and also ask another citizen who earns 5.5 to pay the same amount. What about a person unemployed? How can he pay 5? That's the principle of progressive taxation, the one earning 10 will pay more than the one earning 5, so that the unemployed can still receive some services even if he cannot pay taxes.