Nearly three-quarters of a century ago, walking alone in the Tiergarten through melting snow under the coldly glittering March sun, I determined to write two series of books: one abstract, growing gradually more concrete; the other concrete, growing gradually more abstract. They were to be crowned by a synthesis, combining pure theory with a practical social philosophy. Except for the final synthesis, which still eludes me, I have written these books. They have been acclaimed and praised, and the thoughts of many men and women have been affected by them. To this extent I have succeeded.
Source: The Autobiography of Bertrand Russell, v.3:1944-1969 ,chap4:The Foundation,(1969)
More info.:http://russell-j.com/beginner/AB-POST03.HTM