At its best, science fiction stimulates imagination and creativity. Physically open, psychically open. No doors shut. All the doors stand open, from the pre-human past through the incredible present to the terrible and hopeful future. All connections are possible.
All alternatives are thinkable.
It is not a comfortable, reassuring place. It s a very large house, a very drafty house. But s its the house we live in. And science fiction seems to be the modern literary art which is capable of living in that huge and drafty house, and feeling at home there and playing games up and down the stairs, from basement to attic. Now to define good science fiction.