Volume 4 in the 5-volume series titled Analytical Metaphysics. The essays in this volume are concerned with three main issues. First, what account can be given of the nature of a particular? Second, is identity over time a basic and irreducible relation, or can it be analysed? If so, what is the correct analysis? Third, what account can be offered of what it is to be actual? The final account of this volume involves the claim that actuality is a special property that is possessed by one, and only one, possible world.