What is Life? An Operational Definition

Abstract One way of defining life is via a real definition, which gives the essence of life. Another approach is an operational definition, which shows how living things can be tested or measured in a way that is distinctive of the biological. Although I give a real definition elsewhere, in this paper I provide an operational definition, echoing Canguilhem’s dictum that life is what is capable of making mistakes. Biological mistakes are central to the behaviour of organisms, their parts and sub-systems, and the collections to which they belong. I provide an informal definition of a biological mistake. I contrast mistakes with mere failures and malfunctions. Although closely related phenomena, each is distinct. After giving some brief examples of mistake-making and how it can be tested, I reply to some objections to the very idea of a biological mistake.