"He has a theory, but he has no proof, that his solution is the right one." We use lots of scientific words and phrases in everyday language. Often their usage changes, until their everyday meanings have become completely muddled, and are very different to their scientific definition. Why is a "theory" not just a good idea, and when we ask a scientist for "proof," why can it never be incontestable? This book is aimed at tweens and teens, and explains the difference between the scientific and the everyday meanings of various words.