James Buchanan’s views on public finance have already been analyzed and they are quite well known, as are their origins and roots. However, nothing has ever been said about why Buchanan chose public finance in the first place. The first goal of this paper is to show that Buchanan had made this choice before arriving at Chicago. We show how Carlton C. Sims and Charles P. White influenced him. We also show, by analyzing Buchanan’s M.A. thesis, that he was not only interested in public finance but was also primarily concerned by ethical questions and defended a bureaucratic centralized solution to solve the problem he was discussing – how to share the benefits collected from a gasoline tax among Counties. This helps to understand that Buchanan did not choose to study public finance to learn how to fight government intervention. Quite the contrary: it was to legitimate it. Second, In addition, we also demonstrate that a lot of the ideas that will matter for Buchanan in his career – the importance of ethics and the principle of an equal treatment for equals, the need to link taxes to benefits, the importance to adapt the scale of provision of a public good to the type of public good – were already present in this first work.