Björn Jespersen
TU Delft, Faculty of Technology, Policy and Management, Section of Philosophy
Leiden University, Faculty of Philosophy

Is a broken corkscrew a corkscrew? In general, if x is a malfunctioning F-device, is x then an F-device? The proper-function theorist says Yes, for the proper function of x as an F overrides its malfunctioning as an F. The pragmatist says No, for nothing that fails to function as an F is an F, while anything that does function as an F is an F. I favour an answer in the affirmative, basically because x was designed to function as an F-device. This is not to say, though, that everything that is designed to function as an F is an F. A plan for designing F-devices may be structurally flawed in such a way that nothing manufactured in accordance with it could possibly function as an F-device and, therefore, would not be an F. Our intuitions as to what makes x an F in the first place will strongly influence our intuitions concerning malfunction.

The purpose of my talk is to outline a logical system within which to reason about malfunction. I am going to address the following three issues.

  • formation of the property denoted by the predicate ‘is a malfunctioning F’
  • predication of ‘is a malfunctioning F’ of individual technical artifacts
  • validity, or invalidity, of various arguments in which the predicate ‘is a malfunctioning F’ occurs.

By arguing that a broken corkscrew is still a corkscrew, I have argued that the predicate modifier ‘malfunctioning’ is subsective [roughly, FG(x) / G(x)], hence not privative [roughly, FG(x) / not G(x)]. However, since ‘malfunctioning’, as it occurs in ‘is a malfunctioning F’, is a modifier, it cannot be intersective [roughly, FG(x) / F(x) et G(x)]. Still, we can infer that a broken corkscrew is broken, thanks to the rule of pseudo-detachment, so that we obtain something equivalent to the first conjunct of F(x) et G(x). The rule says, roughly: FG(x) / *F(x). In words, “a malfunctioning F malfunctions”. The idea behind the rule is to convert an attributive occurrence of ‘malfunctioning’, e.g., ‘F’, into a predicative occurrence, ‘F*’. The rule of pseudo-detachment has been developed together with Pavel Materna and Marie Duží. It forms part of a general project on intensional logic, which is in this case applied to properties and the phenomenon of predicate modification.