 Kant’s injunction to look to the mere form of law at first appears to provide no guidance at all, and has often been reproached on this basis. Defenders of Kant’s ethics argue that it represents a substantial constraint: to avoid all those ways of thinking and acting that cannot be followed by all. (For discussion see inter alia O’Neill 1989: Ch. 5; Herman 1993; Allison 1990: Ch. 10 §II.) If so, the autonomy of reason can point to the positive sense of freedom at the heart of Kant’s practical philosophy (cf. Brandom 1979). This is the possibility of acting in ways that do not rely on “contingent, subjective conditions that distinguish one rational being from another” (5:21), and hence do not fall foul of others’ demands for justification.