The best-known sentence from Grotius's treatise On the Law of War and Peace (De iure belli ac pacis, 1625) is found in the Prolegomena,
that is, in the introduction, where Grotius says: ?What we have been saying [about the signification of the word “law” (jus)] would have a degree of validity even if we should concede that which cannot be conceded without the utmost wickedness, that there is no God, or that the affairs of men are of no concern to Him'.1 This statement, known as the ?impious hypothesis', and in particular the phrase ?even if we should concede' (etiamsi daremus), has inspired a heated discussion about whether Grotius conceives of the foundation of the natural law (jus naturae) in secular or in theological terms.[653] [654] A secular interpretation would imply that Grotius develops a system of natural law that is not based on and does not presuppose the tenets of the Christian religion. It would make Grotius the first post-medieval thinker who tried to create a fully secular theory of natural law.[655] Proponents of the theological interpretation, on the other hand, point out that the sentence quoted above implies a thought experiment, a speculation of the kind frequently encountered in scholastic writings.[656] According to these interpreters, it is hard to see what Grotius's innovative approach might consist in. The ?impious hypothesis' is, like many other similarly famous sayings, often quoted out of context. What tends to be neglected is the fact that the sentence is part of a larger argument presented in the Prolegomena and its meaning is codetermined by this context. In the first part of this study, we aim to explain the meaning of the impious hypothesis, by taking into account what Grotius says about natural law in the treatise proper, especially in Book ι. It is there that Grotius defines natural law and distinguishes it from other kinds of law. Grotius's ambitions in On the Law of War and Peace are legal rather than philosophical. His goal is to show how, using the ?first principles', such as his rudimentary theory of human sociability and natural law, the entire system of law could be laid out or reformed, how the various existing legal relationships - for instance property, family, slavery, etc. - could be incorporated, to create space for ordering the practical relations between states and nations. These aims significantly contributed to the popularity of Grotius's treatise, especially in Protestant countries.[658] A scholar of philosophical inclinations, however, has to face the fact that Grotius says very little about the abovementioned ?first principles'. His scattered remarks on this subject are open to varying interpretations. With full awareness of this challenge, let us now turn our attention to Grotius's argument in the Prolegomena. 1