Philosophical theories often hinge on claims about what is necessary or possible. But what are possibilities and necessities, and how could we come to know about them? This book aims to help demystify the methodology of philosophy, by treating such claims not as attempted descriptions of strange facts or distant 'possible worlds', but rather as ways of expressing rules or norms. Thomasson is a gifted writer and philosopher, with a distinctive voice and a forceful message. Norms and Necessity is important and timely, making a strong contribution to one of philosophy's central problems. In support of that verdict I would say that it is the clearest and best-researched work on the nature of modality--the philosophical problems surrounding notions of necessity and possibility--to appear since Saul Kripke and David Lewis put modality back into the centre of the philosophical landscape some fifty years ago. It marks a radical departure from the tradition that they inspired, which makes it especially important.