Intelligence is an extremely subtle concept. It’s a kind of understanding that flourishes if it’s combined with a good memory, but exists anyway even in the absence of good memory. It’s the ability to draw consequences from causes, to make correct inferences, to foresee what might be the result, to work out logical problems, to be reasonable, rational, to have the ability to understand the solution from perhaps insufficient information. You know when a person is intelligent, but you can be easily fooled if you are not yourself intelligent.
Excerpt from an interview with scientist and author Isaac Asimov (1919-1992) in Conversations with Isaac Asimov edited by Carl Freedman, University Press of Mississippi (2005). Asimov was amazingly prolific during his career, having written and edited more than 500 books in the diverse fields of popular science, mathematics, astronomy, science fiction, and literary criticism. Asimov published popular authoritative guides to the works of Shakespeare and the Bible.