This book, first published in 1987, examines the notion of truth and then discusses knowledge and the way in which much of our knowledge revises or rejects the common-sense we start from. The author argues that our knowledge is not as secure as some would like to think and that there are important limits to the possibility for explanation. He shows how values permeate our ordinary thinking and argues against the objectivity of these values, showing the practical consequences of this argument for teaching in schools.