Wittgenstein's dictum in 580 of Philosophical Investigations, ‘An “inner process” stands in need of outward criteria’, is one of his most frequently mentioned remarks, and is largely treated as a particularly clear and unproblematic statement, at least as Wittgenstein's sayings go. When anyone finds it unproblematic, he naturally does not say what he takes it to mean; but if it is as mystifying as I will claim, and if its meaning is as well concealed as I will suggest, it is almost certain that it has been widely and seriously misunderstood.