Language is commonly taken to be one of the unmistakable manifestations of human intelligence. Anyone who can read and understand this sentence is assumed to be not only literate (since it is an English sentence) but also rational (i.e. able to evaluate the propositions expressed). But the justification of those assumptions raises a number of philosophical difficulties which it is the purpose of this book to explore. It argues that intelligence is nothing more than a lay term for the various forms of integration that are involved in human activities. The current confusions that surround intelligence are primarily due to psychologists' rash claims to be able to 'measure' it.