Ed Greenwood

When, who, and what things happen to becomes meaningful, then what happens starts to matter, and play can evoke strong emotions, fierce and ongoing urges to succeed, and a desire to leave a mark, drive meaningful change, or build lasting institutions.

The historical novelist has to consider what has actually happened, while the SF writer is dealing in possibilities, but they are both in the business of imagining a world unlike our own and yet connected to it.