A Device-Oriented Defi nition of Functions of Artifacts and Its Perspectives 209
of an accidental function requires the screwdriver’s capacity to perform the hitting function
based on its physical feature, that is, a fl at hard surface. The screwing function could be
performed by a key as its accidental function. The hitting function is an essential function
of a hammer.
Such capacities to perform accidental functions induced by accidental use, in principle,
cannot be enumerated completely before used in reality. Note that the variety of accidental
functions as local functions (discussed in section 12.2.2) are limited to those related to
possible behaviors, unlike possible (unlimited) conjunct functions such as the screw-
driver’s accidental function using a nail for two pieces of wood.
The distinction between essential and accidental functions discussed thus far
pertains to external functions, which are determined by a user. We can also consider
distinctions among the component functions of components embedded in a system.
A component is designed and manufactured for a specifi c function, which is its essential
function. When a component is integrated into a system, a designer of the system
normally uses a component to achieve its essential function. However, it is possible that
the system’s designer uses a component to fulfi ll a function different from its essential
function. For example, a slurry containing diamond powder is manufactured for improving
cutting effi ciency. However, in a cutting device a slurry can also be used for cooling
the cutting blade. In this case the slurry performs a cooling function as an accidental
function.
Such accidental use is distinguished from a (proper) function in some philosophical
writings (e.g., Wright 1973; Perlman 2004; Preston this volume). Such accidental use is
called “function-as.” We regard an accidental effect as a function if it is intended by a user
in a specifi c context or if it is recognized in a context of a system’s goal. If not, it is a
behavior. One of our justifi cations for our use of the term function here is the effect-ori-
ented defi nition from the engineering viewpoint. As actual effects, an essential function
and an accidental function can have the same intended effect for users in our engineering
sense. The second justifi cation is to detach a function from a function performer such as
a required function without a function performer, as discussed in section 12.2.4. A required
function can be fulfi lled as either an essential function or an accidental function. The third
justifi cation is that our function statements are mainly “weak function statements” (Boorse
2002), in contrast to “strong function statements” for which the proper functions are dis-
cussed. In fact Boorse does not distinguish a function’s performance by accident in his
“weak function statement.”
Preston, in this volume, discusses “unintended proper functions” and “phantom func-
tions” as diffi culties of the qualifi cation of intended use. Many examples for the former
can be found with respect to social, economic, or political uses. The latter have no physical
effects. Our defi nition of base-functions is based on physical and actual behavior, which
excludes those cases (as a prescriptive defi nition).