The previous chapter discussed the problem of speaking for others. This one turns to the question of how we can speak about others, how we can understand what their pain means to them, when it is not commensurable with our own. Or even more radically: How can I know that someone else is in pain, let alone have any real knowledge of what that pain feels like? Wittgenstein answers these questions with breathtaking directness. Neither dismissing nor solving the problem, he tells us all we can know and all we need to know: ‘If I see someone writhing in pain with evident cause I do not think: all the same, his feelings are hidden from me’ (Philosophical Investigations, p. 223). I can doubt most things if I put my mind to it; and of course I cannot know precisely how another's pain feels. But if I see a woman who has been hit by a truck, it would be better to call an ambulance than to consider the merits of philosophical scepticism. As Wittgenstein puts it in another passage, ‘Just try – in a real case – to doubt someone else's fear or pain’ (Philosophical Investigations, p. 102). We cannot directly share it, but we know it when we see it.

The case of trauma and of trauma texts nevertheless complicates the recognition of the other's pain. Wittgenstein refers to suffering which is visible (‘I see someone writhing in pain’) and has ‘evident cause’. Its source and its signs cannot be misinterpreted: the truck hit the woman and she is crying in pain. The causes and symptoms of trauma, however, are less obviously manifest and more easily mistakable. This is suggested in one of the most frequently quoted passages in trauma studies, where Freud describes the survivor of a train crash in Moses and Monotheism: