
“It's a system for testing your thoughts against the universe and seeing whether they match.”
Interview by Bill Moyers on Bill Moyers' World Of Ideas (21 October 1988); transcript http://www-tc.pbs.org/moyers/faithandreason/print/pdfs/woi%20asimov2.pdf (pages 5-6)
General sources
Context: Science doesn't purvey absolute truth. Science is a mechanism. It's a way of trying to improve your knowledge of nature. It's a system for testing your thoughts against the universe and seeing whether they match. And this works, not just for the ordinary aspects of science, but for all of life. I should think people would want to know that what they know is truly what the universe is like, or at least as close as they can get to it.