Originally delivered as a speech at the Philadelphia Science Fiction Conference, November 9, 1968. Copyright 1969 by SFWA.
| Date | Publication | Publisher | Type | Page | |
|---|---|---|---|---|---|
| February 1977 |
|
Turning Points: Essays on the Art of Science Fiction | Harper & Row | Nonfiction | 132 |
| May 2014 |
|
Turning Points: Essays on the Art of Science Fiction | Gateway / Orion | Nonfiction |