A simple model of linear taxation is used to single out different types of tax equilibria. Sufficient conditions for national income to be a decreasing function of the marginal tax rate are given for each case. Equilibria are classified according to whether: (i) aggregate labor supply is forward bending, (ii) aggregate labor supply is backward bending, (iii) the equilibrium is a welfare maximum, and (iv) the equilibrium is a "political equilibrium".