Raymond Tallis's The Explicit Animal (1991) was a passionate attack on attempts to explain human consciousness in purely biological terms. This ground-breaking book defended the distinctive nature of human consciousness against the misrepresentations of those many philosophers and cognitive scientists who aimed to reduce it to a set of functions understood in evolutionary, neurobiological and computational terms. In his laudatory review in The Times Literary Supplement, Stephen Clark expressed the hope that Tallis would continue his explorations. On the Edge of Certainty does precisely that, investigating and clarifying the implications of the highly original view of human nature discussed in his earlier book, in order to understand the nature of truth, of language, of the mind and of the self.