You came to this book assuming that the basic units of human cognition are states such as thoughts, beliefs, perceptions, desires, and preferences. That assumption is natural enough: it is built into the vocabulary of every natural language. And each state is typically identified by way of a specific sentence in one’s natural language: one has the belief that P, or the desire that Q, for example, where P and Q are sentences. Human cognition is thus commonsensically portrayed as a dance of sentential or propositional states, with the basic unit of computation being the inference from several such states to some further sentential state. ¶ These assumptions are central elements in our standard conception of human cognitive activity, a conception often called “folk psychology” to acknowledge it as the common property of folks generally. Their universality notwithstanding, these bedrock assumptions are probably mistaken.