In his inaugural lecture, Peter Mascini takes issue with the goal of scientific purity in the behavioral study of law, conceived as the deliberate choice to postulate a limited number of universally applicable behavioral principles. The guiding principle of behavioral sociology is that law behaves in correspondence to social space, while the guiding principle of law and economics is that individuals behave rationally. Behavioral economics has challenged the principle of the rational actor and, consequently, has also challenged the desire for scientific purity in law and economics.Peter Mascini defends a two-fold thesis: first, that the purification of sociology proposed by behavioral sociology is a blind alley that can only be exited by allowing impurity. Second, that the behavioral economics movement has offered law and economics an opportunity to reinvigorate by embracing impurity. The combination of the two parts of his thesis lead him to the claim that we need less purity in the behavioral study of law rather than more. He ends his lecture by stating that the introduction of impurity that has been started by behavioral economics needs to be extended in several respects. He will propose to replace the behavioral study of law by an approach that not only takes empirical research seriously, but also adopts a modest attitude by surrendering the ambition to come up with universally applicable predictions and by taking seriously meaningful behavior.