Benefit approach principle: the amount of taxes a person should pay by the benefits received in public services.
Equal sacrifice theory: the surrender of equal measures of utility by taxpayers. Equal sacrifice theory has three sub-groups:
1. Equal absolute sacrifice (where each taxpayer surrenders the same absolute degree of utility that he obtains from his income).
2. Equal proportional sacrifice (where each sacrifices the same proportion of utility he receives from his income).3. Equal marginal sacrifice (where each gives up the same utility from the last unit of income)