It is still underestimated to what extent in his main works Hugo Grotius not only sketched and developed a system of private, state and international law; but also outlined a general philosophy or theory of law. By asking questions concerning the law of property, the law of prize and booty, the law of peace and war or the legal status of sovereignty he did not only refer to the 'right side', i.e. to actions that can be labelled as rightful and legal. He also dealt with many aspects of what is not right and unlawful, not limiting himself to just give mere examples of crossing the border to the 'non right side'. It was a part of Grotius's methodological approach to systematically reflect on the law from the perspective of its violations. One example of such a violation is the act of piracy and the figure of the pirate. To outline this is the aim of the following article. By showing that the pirate and his 'legal twin', the privateer, were belong together as two sides of the same coin, they come to symbolise in an exemplary way the differentiation between 'right' and 'non right' as the unity of law in the legal philosophy of Grotius.