 Scanlon himself may understand trusteeship merely as a way of realizing or respecting the full moral status of human beings with radical impairments, a status that is based on “the ties of birth.” Other philosophers, however, suggest that trusteeship can secure full moral status by helping to satisfy criteria that could not otherwise be met. Thus, Francis and Silvers (Francis 2009; Silvers and Francis 2009) argue that cognitively normal human beings can function as “mental prostheses” for radically impaired ones: