This is a collection of eight lectures delivered between 1946 and 1955. They are a record of the change and growth over 10 years in the thinking of one of the outstanding scholars of his generation. The entire book is thus an illustration of its central statement of the values to society of the open mind. Here is the author's definition of his belief in this: :An indispensable, perhaps the indispensable, element in giving meaning to the dignity of man, and in the making possible the taking of decision on the basis of honest conviction, is the openness of men's minds, and the openness of whatever media there are for communion between men, free of restraint, free of repression, and free even of that most pervasive of all restraints, that of status and hierarchy.