Capacity is decision-specific and time-specific, and the bar for it moves with what is at stake. When it is gone, someone else decides — but not by their own lights. Assess Mr Doyle's four abilities against a sliding scale, then switch modes and watch how much the surrogate ladder depends on evidence you may not have.
Mr Doyle, 61. Long-standing schizophrenia, stable on clozapine for years. End-stage kidney disease. The renal team wants to start haemodialysis. He is calm, oriented and articulate, and the nurse who has known him for six years says he seems himself.
What is riding on this decision?
And which way is he going?
Pick what he actually says
Mrs Doyle, 84. Advanced dementia, admitted from a nursing home with aspiration pneumonia and now septic. She cannot understand, appreciate, reason or express a choice about anything. The question is a feeding tube. Her son and daughter are at the bedside. Toggle on whatever you actually have.