Patient and public involvement in health research, including mental health research, is promoted by research funders in England. However, it is poorly conceptualised. One argument is that patient and public involvement in research is an ethical imperative because those who research is for should have a stake in how it is done. This could be developed through concepts of citizenship and democratic science. More strongly, it can be argued that changing the knowledge producers will change knowledge itself. Starting with feminist standpoint epistemology, it is argued that a political conceptualisation best captures the new knowledge that marginalised health groups can produce.