Kant offers the following argument for the formula of humanity (FH): Each rational agent necessarily conceives of her own rational nature as an end in itself and does so on the same grounds as every other rational agent, so all rational agents must conceive of one another's rational nature as an end in itself. As it stands, the argument appears to be question-begging and fallacious. Drawing on resources from the formula of universal law (FUL) and Kant's claims about the primacy (...) of duties to oneself, I propose a contractualist reconstruction of this puzzling line of reasoning. (shrink)