"Philosophy begins on the ground with the concrete reality of lived experience. Experience provides us with the raw data for our theories. Then, our thought takes off, losing contact with the ground and soaring into heights of imaginative speculation. During speculation, we use rational criteria and imagination to synthesize facts into a (relatively) systematic worldview. In the end, however, our theories must eventually land and once again make contact with the ground—our speculations and hypotheses must ultimately answer once again to the authority of experience."
- Process and Reality: An Essay in Cosmology; Gifford Lectures Delivered in 1930 By Alfred North Whitehead published by Macmillan & Co.