In this chapter, I clarify what it is for a composite object to exist at a time and over time by analyzing the conditions under which things compose it at a time and over time. Some things, the xs, make up an object, O, at a time t1 if and only if the xs are maximally bonded then, which is to say that the xs are simply bonded, clinging together, and include everything simply bonded to any of the xs. The object O that is composed of the xs at one time may be made up of other things at a subsequent time. Over time, however, objects may change in composition only incrementally (unless we allow for the possibility of an object being disassembled then reassembled). Incremental changes are ones in which the mass of what is added (removed) is small as compared to the object’s mass before the addition (removal).

This chapter introduces the book. What may we become? What is the significance of extinction? This book addresses these questions after clarifying what persons, species, organisms, and material objects are. Like you, I am an organism, but also a material object. I could survive, remaining that same object, after it stops being a human organism.

In his 1925 paper ‘A Defence of Common Sense’, G. E. Moore set out his ‘Common Sense view of the World’ as a series of ‘truisms’ about himself and the world. Moore then claims (1) that our common-sense truisms are largely true, and (2) that we know that our common-sense truisms are largely true. In his writings Moore defends (1) against philosophers who argue that common sense is no guide to the nature of reality by distinguishing between the ordinary meaning of his common-sense truisms (which is unproblematic) and their analysis (which is often doubtful). He defends (2) against sceptics by arguing that the assessment of claims to knowledge has to respect the framework of deep common-sense beliefs which shape our evidence. This chapter argues that Moore’s defence of (1) is not persuasive but that the defence of (2) includes important contributions to epistemology.