Most philosophers adopt an etiological conception of functions, but not one that uniformly explains the functions attributed to material entities irrespective of whether they are natural or man-made. Here, I investigate the widespread idea that a combination of the two current etiological theories, SEL and INT, can offer a satisfactory account of the proper functions of both organisms and artifacts. (Roughly, SEL equates a function with a selected effect and INT with an intentional content). Making explicit what a realist theory of function supposes, I first show that SEL offers a realist theory of biological functions in which these are objective properties of a peculiar sort. I argue next that an artifact function demonstrates the same objective nature as a biological function when it is accounted for by SEL, but not when it is accounted for by INT. I explain why a dual theory of artifact functions admitting both INT and SEL functions is to be dismissed. I establish that neither INT nor SEL alone can account for all artifact functions. Drawing the conclusion that we need a new etiological theory of function, I show how one can overcome the apparent inevitability of INT for some artifact functions. Finally, I outline a new etiological theory of functions that applies equally to biological entities and to artifacts.
