 This means, Strawson claims, that one can only ascribe mental states to oneself if one is capable of ascribing them to others which, in turn, means that I cannot have gained the capacity to think of others’ mental states by means of an analogical reasoning from my own case. This, Strawson argues, shows that others’ observable behaviour is not a “sign” of their mentality, but is a “criterion” of it. In short, we must have knowledge of others’ minds if we are self-conscious (for the full argument, see P.F. Strawson 1959: 105ff; for critical discussion, see R. Stern 2000: ch. 6; Sacks 2005; Joel Smith 2011).