 Robert Stalnaker (2008) raises further doubts regarding Perry’s treatment of Mary’s new knowledge. Drawing on a distinction between the two stages of Mary’s epistemic progress (see Section 3.3 above), he argues that the cases of acquiring demonstrative beliefs which Perry compares with Mary’s new knowledge are akin to the second stage of Mary’s progress, but “It is at stage one that the problematic cognitive achievement – the learning ‘what it is like’ to see red – takes place” (2008, 44).