The Inherent Normativity of Functions in Biology and Technology 105
7.2 Rival Theories of Function
It is common to distinguish two general approaches to characterize the notion of function.
On the one hand, there is the causal-role or causal-contribution (CR) view, fi rst proposed
by Cummins (1975). According to this view, the function of an item is the causal contribu-
tion that this item makes to a capacity to show a certain behavior of a larger entity, of
which the contributing item is a component, in the ordinary, mereological sense. On the
other hand, we have the etiological theory, or theory class, of which Wright’s (1973) theory
was the fi rst representative. A decade later, however, Millikan’s (1984) much more sophis-
ticated theory of proper functions (PF) replaced Wright’s proposal as the most general
articulation of this view. It restricts the attribution of functions to items that are, in a precise
technical sense, reproduced.
These two approaches to the notion of “function” can be distinguished by the sort of
explanatory work that they make the concept of “function” do. The attribution of a func-
tion as a causal contribution answers a “how” question: how does a particular entity
achieve a certain behavior? An answer that refers to the contribution of components of the
entity implies that this entity is complex or systemlike. For noncomplex entities, the ques-
tion of how its behavior comes about seems pointless; anything to be said about it can
refer only directly to the laws of nature that it is subject to. On an etiological theory, in
contrast, the attribution of a function is usually said to answer a “why” question: why does
a particular item exist? The attribution of a function to the item is a sort of summary of
the relevant causal history of the item, usually but not necessarily as part of a larger
entity.^1
Both the CR and the etiological theories occur in more specialized versions.^2 A special
case of the causal-role theory is Boorse’s (2002) goal-contribution (GC) theory. It limits
the attribution of functions to the components of goal-directed systems instead of just any
system, but maintains the basic outlook of the causal-role theory that functions are the
causal contributions to the system’s capacities, ultimately, in the case of the goal-directed
systems that are called living systems, the capacity to survive and reproduce.^3
Recently another variant of the causal-role theory has been proposed by Krohs (2004;
forthcoming). It limits the attribution of functions to the components of systems-with-a-
design (SD), where the relevant notion of “design” is an extension of the ordinary concept,
which refers to intentional design by human beings. A system has a design in this extended
sense if, roughly, its components are picked, by whatever mechanism, to become compo-
nents on the basis of the fact that they are tokens of a particular type, rather than by their
individual physical properties.
A special case of the etiological theory, and in particular the PF theory, is the selected-
effect (SE) theory as advocated by, for example, Neander (1991). By specifying in the
defi nition of function a particular causal mechanism through which an item’s current pres-
ence is historically explained, being the Darwinian theory of natural selection, the SE