Lack of clarity about the uses of the word why is responsible for confusion on a number of philosophical fronts. In this entry we shall confine ourselves to two groups of topics where greater attention to the proper and improper behavior of this word might well have avoided the adoption of misguided theories. There is, first, the contrast, or the alleged contrast, between the "how" and the "why" and the view, shared by writers of very different backgrounds, that science can deal only with how-questions. Second, there are certain "ultimate" or "cosmic" questions, such as "Why do we exist?" or, more radically. "Why does the world exist?" or "Why is there something rather than nothing?" Some, like Arthur Schopenhauer and Julian Huxley, regard these questions as unanswerable; others, like Étienne Gilson and F. C. Copleston, believe that they can be answered; but whether these questions can be answered...