 It may then be recognized that the unobserved event was absolutely identical to an event which did not occur at all.Of course, the fact that the tree is known to have changed state from 'upright' to 'fallen' implies that the event must be observed to ask the question at all – even if only by the supposed deaf onlooker.The British philosopher of science Roy Bhaskar, credited with developing critical realism has argued, in apparent reference to this riddle, that