What is death? It will surely seem appropriate to address this question in a book like this. It is, after all, a book about death. And so it is a book about a subject that is of considerable interest to all of us, as it has been for thousands of years. It may well seem appropriate, then, to address the question more widely, and to recognize that this is not simply of philosophical but of quite general concern. And I shall ask, and give an answer to, the question here. There is a second question. Does it matter that we discover what death is? It might simply be taken for granted that this does matter, and that it is not only here appropriate, but also generally important to ask and to answer this first question. So it might be thought that this second question is not one that needs in any further way to be addressed. But, of course, mattering comes in degrees, and the “we” of the question might be philosophers, or other people having a professional interest in death, or those – surely almost everyone – having a non-professional interest in the matter. As the question cannot then, have a simple yes/no answer, I shall consider it and give it in the end a less simple answer here.

What is death? I shall say that it is the irreversible breakdown of, or loss of function in, the organism as a whole.