 On the face of it, some laws have other functions. A requirement that “a will must be signed” generally imposes no duty—not a duty to make a will, and not even a duty to have it signed if you do—it sets conditions in the absence of which the document simply does not count as a valid will. Nonetheless, some philosophers argue that the content of every legal system can and should be represented solely in terms of duty-imposing and duty-excepting laws (Bentham Of Laws in General; Kelsen 1960 [1967]). Bentham asks,