Proxy consent and counterfactual wishes

I discuss conditions for the validity of proxy consent to treatment on behalf of an incompetent person. I distinguish those incompetents who, when previously competent, expressed an opinion on the treatment in question from those who were never competent or who, though previously competent, never expressed an opinion on the proposed treatment. In the former case valid proxy consent usually requires respecting the stated wishes of the patient. The latter case is more difficult. I consider a widely-held principle which appeals to the counterfactual wishes of the incompetent person. I argue that it is unacceptable and propose in its place a principle having to do with the best interests of the patient.