210 Yoshinobu Kitamura and Riichiro Mizoguchi
12.2.6 A Brief Comparison with Biological Functions
The characteristics of the functions of technical artifacts are very different from those of
biological organs. A biological organ performs its component function in a biological
system under fi xed context(s). For example, a component function of a heart is to increase
the pressure of fl owing fl uid (blood) in the system context of the circulatory system. This
is the same function as a pump. The component function of the circulatory (sub)system is
to transport substances.
As pointed out in Johansson and colleagues (2005), a biological organ can perform
multiple functions in a system. Those functions sometimes contribute to the functions of
different subsystems (e.g., the oropharynx’s functions; cf. Johansson et al. 2005). However,
their system contexts are fi xed to the organ and do not change. Thus a component function
of a biological organ is rather tightly associated with the organ (unlike the component
functions of engineering artifacts). In a fi xed context a component function in a system
contributes to the achievement of a goal of the system. Such contribution is shared with
technical artifacts.
As external functions, a biological organ can perform several functions according to the
given use contexts in the same manner as artifacts. For example, a nose can perform the
external function of supporting glasses. We also view that a heart can perform a sound-
making (heart sounds) function as an external function under the context of medical
diagnosis whereby a medical doctor listens to heart sounds.^4
The essentiality (i.e., whether it is an essential or accidental function) of such external
functions of biological organs or organisms is out of the scope of our discussion here. As
pointed out in McLaughlin (2001: 144), “the organisms are not attributed functions... only
their traits or parts have functions.”
In Johansson and colleagues (2005), a function of a biological organ is defi ned as “a
disposition to act in a certain way to contribute to the realization of [a.. .] larger function
on the part of that whole organism which is its host.” This defi nition shares with our defi -
nition the “goal-oriented”-ness of a function and the agent’s inherent property to perform
a function. This defi nition, however, excludes accidental functions and says a function
“inheres” in the entity (called “function bearer”), which can be regarded as a refl ection of
the characteristics of functions of biological organs as discussed earlier in this section.
Thus it roughly corresponds to the “capacity to perform a function” in section 12.2.4,
though a disposition (proneness) is different from a capacity. In fact Johansson and col-
leagues (2005) distinguish function from functioning. Our defi nition for engineering
devices aims at a conceptualization of function separated from a function bearer, as dis-
cussed in section 12.2.5. It comes from an engineering requirement, that is, a function’s
independence of realization. The defi nition by Johansson and colleagues (2005) also
includes the reliability of performing the function.