An attempt to define intelligence appears in the 1996 article Intelligence: Knowns and unknowns" in American Psychologist. The authors implied it is “ability to understand complex ideas, to adapt effectively to the environment, to learn from experience, to engage in various forms of reasoning, to overcome obstacles by taking thought.” James Flynn has a 2009 book What is Intelligence? If it takes a book to discuss the meaning of a word, maybe the word is too vague to quality as a definable concept or as a scientific concept. Are there any updates to the 1996 attempt to define intelligence?