 Life-functionalism, a view introduced by Aristotle, analyzes the property alive in terms of one or more salient functions that living things typically are able to perform. The salient functions Aristotle listed were nutrition, reproduction, sensation, autonomous motion, and thought. However, life-functionists disagree about how to formulate their account and about which functions are salient. Take Aristotle’s list. Obviously, it would be a mistake to say that something is alive if and only if it can perform all of the functions on the list. Might we say that, for something to be alive, it suffices that it be capable of one or more of the listed functions? Is being capable of one of these functions in particular necessary for something to be alive? As Fred Feldman points out, neither of the suggestions just mentioned is acceptable.  Devices such as Roomba cleaning robots can do one of Aristotle’s functions, namely move themselves, but are not alive, so being able to do at least one listed function does not suffice for being alive. Nor is it plausible to say that any one on the list is necessary for being alive.  Which on the list would this necessary function be?  Perhaps nutrition?  Adult silk moths are alive but lack a digestive system, so are incapable of nutrition. And, as many theorists have noticed, many living things cannot reproduce; examples include organisms whose reproductive organs are damaged and hybrid animals such as mules.