Abstract:This paper examines whether a one-book-system that takes the commercial law profit definition as tax base (the so-called authoritative principle) is adequate from an evolutionary point of view. We consider firstly the case that European International Financial Reporting Standards (EU-IFRS) are relevant for all statements with the authoritative principle based on EU-IFRS. Secondly, we examine the fact that EU-IFRS focus on the consolidated annual accounts and that the national accounting principles are relevant for individual statements. Tax law analysis under genuine uncertainty requires a framework and we present such a framework. It entails an interpretation of equality of taxation, a hypothesis on the functioning of markets, an interpretation of realizable and desirable market goals, tax effects hypotheses, and action hypotheses for personal and corporate companies under genuine uncertainty. Contrary to the mainstream of accounting literature, from our evolutionary point of view, the authoritative principle is adequate. The reason is that commercial profit is an adequate instrument to achieving the tax goal equality of taxation in the sense of reducing expectable tax avoidance decisions. This is the case because according to evolutionary action hypotheses as well as tax effects hypotheses, commercial profit can be a subjectively rational decision criterion for personal and corporate companies alike. Equality of taxation is for its part in line with the evolutionarily interpreted social values freedom of choice and equality before the law. Since we focus on the question if the existing commercial profit concept can be an adequate tax base, we do not discuss whether we would have more reasons to take a conservative profit concept as tax base rather than EU-IFRS. Just as little, we analyze whether it is better to take EU-IFRS profit as tax base although national accounting principles are relevant for individual statements.Keywords: ability to pay-principle, authoritative principle, equality of taxation, evolutionary tax effects hypotheses, evolutionary analysis of tax law, horizontal equity, vertical equity JEL classification: B53, K34, M48