The longest chapter of the book is dedicated to Kant’s core argument against Constant. Kant’s essay contains three formulations of the same idea: that lying, or a right to lie, would undermine the possibility of contracts, and of the duties and rights that contracts generate. Kant is convinced that this would be disastrous for humankind. That is why he claims, against Constant, that lying – not an unconditional duty of truthfulness – would be the downfall of society. The chapter discusses the enigmatic notion of a ‘source’ of right or rights (which should not, it is argued, be equated with the social or original contract); and it subjects two slightly different reconstructions of the core argument to philosophical scrutiny, concluding that both are untenable. It seems that, in 1797, Kant revived Michaelis’s argument, which he had appropriated and then abandoned earlier in his philosophical development. This negative result does not, however, lessen Kant’s absolutism because the ethical duty of truthfulness is still in place.