We have tried to show both the movement and the conflict of ideas. Even one man may hold ideas which go oddly together , as the ideas of Newton did ; or which change sharply between youth and age, as those of Hobbes did: or which at bottom are inconsistent, as those of Rousseau were. In a community the conflict of ideas has a special fore: established ideas held rigidly for social reasons or for reasons of interest are at odds with new ideas, and the character of the community derives from the struggle and balance between these. We have wanted to show the creative value of the conflict of ideas.
Yet, the evolution of an idea also has an inner logic, which it follows through every conflict. Consider, for example, how the idea of progress has changed and yet has retained its direction through the four centuries which we study. We have been at pains to trace this logic of ideas through their changes; and we draw attention, as one example, to our extended discussion of the idea of man 's unity with nature, which we follow from the simple materialism of Hobbes to Kant's subtle theory of scientific knowledge.
In the four centuries which this book covers, the world has been transformed from medieval to modern. They are centuries of change, in every detail of life; and the history of their ideas, as we have said, is necessarily a history of movement. The movement is created by that which gives life to ideas: by the interplay of all the interests of the mind, by the pressure of events, and by the expression of personalities. It is this sense of movement, of ideas felt as the mind in action, which we have wanted to communicate. To us, the Age of Enlightenment-to take a single example-is not a restful abstraction. It is a complex of people and groups with conflicting ideas which yet have a common direction; and this is why we see it and present it under a new name, as the Age of Reasoned Dissent. This is our approach to the intellectual history of all the periods that we cover.