In An Autobiography, R.G. Collingwood offers a strikingly compact reductio ad absurdum of John Cook Wilson's metaphysical realism. Cook Wilson formulates the thesis as the inefficacy of epistemic states to determine the properties of objects of knowledge. He explains realism, according to Collingwood, as the view that 'knowing makes no difference to what is known'. Collingwood objects that any such formulation is 'meaningless'. The problem is that by implication the metaphysical realist is supposed to know that Cook Wilson's principle is true, which requires the realist per impossibile to know what something is like even when its properties are unknown.