Thesis 1 In order to optimize equity and equality in the application of income taxes in the 21. Century the ability-to-pay principle still is the most adequate guide.

Thesis 2 A wealth tax cannot be justified if the perso- nal income tax has been based on a compre- hensive notion of income from capital.

Thesis 3 A personal income tax based on a notion of income from capital that does not make any difference between entrepreneurs and investors, should give all shareholders a relief for the corporate income tax in order to avoid economic double taxation on the profits of the corporation.

Thesis 4 Given a tax base comprising real income from labour and enterprise, the implemen- tation for all private property of fictitious income at a different rate is in conflict with the ability-to-pay principle.

Thesis 5 The accrual method is, for taxpayers as well as for the tax authorities, the most bene- volent method to determine income from capital.

Thesis 6 Deferral is not necessarily in conflict with horizontal and vertical equity or with the notion of economic efficiency.

Thesis 7 Capital gains should be included in the general income taxation scheme. Special (business) reliefs can be justified for rein- vestment and to prevent the break up of businesses. However, departing from a reali- zation concept with respect to the notion of income, as a main rule, capital losses should only be compensated with capital income, including capital gains.

Thesis 8 In a civilized income tax regime inflation neutrality is indispensable. The method of compensation for inflation should be struc- tural and equal for all types of income. Scientists should produce a method that is theoretically acceptable and feasible at the same time. This method could be optional for taxpayers.