Abstract
Tylman (Found Sci, 2017) has recently pointed out some striking conceptual and methodological analogies between philosophy and computer science. In this paper, I focus on one of Tylman’s most convincing cases, viz. the similarity between Plato’s theory of Ideas and the object-oriented programming (OOP) paradigm, and analyze it in some more detail. In particular, I argue that the (Neo)platonic doctrine of the Porphyrian tree corresponds to the fact that most object-oriented programming languages do not support multiple inheritance. This analysis further reinforces Tylman’s point regarding the conceptual continuity between classical metaphysical theorizing and contemporary computer science.
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Notes
The historical development of the Porphyrian tree is surprisingly similar to that of another logical diagram, viz. the square of opposition. The theory embodied by this diagram was first expounded by Aristotle, but the actual diagram was only constructed by a later commentator (Apuleius, 2nd century CE). It, too, was highly popular among medieval logicians and is nowadays still used in logic and philosophy, but also in various other disciplines, including linguistics and computer science (Parsons 2012; Smessaert and Demey 2014, 2015; Demey and Smessaert 2016, 2017).
For reasons of space, I will not go into the details of these various programming languages. However, it should be mentioned that some of these languages do support some ‘lightweight version’ of multiple inheritance. For example, in Java, a class is not allowed to inherit from multiple superclasses, but it is allowed to implement multiple interfaces (Gosling et al. 2015). Finally, there also exist languages that fully support multiple inheritance, such as C++, Python and Perl.
A similar issue arises in non-monotonic logic, where it is sometimes called the ‘Nixon diamond’ (Strasser and Antonelli 2016): consider the defeasible statements that Quakers are usually pacifists (cf. class B with one method) and that Republicans are usually not pacifists (cf. class C with a conflicting method). Given that Richard Nixon happens to be both a Quaker and a Republican (cf. class D inheriting from both B and C), it is not at all clear whether we should conclude that he is or that he is not a pacifist.
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Acknowledgements
I would like to thank Hans Smessaert, Margaux Smets, Wouter Termont, Leander Vignero and two anonymous referees for their helpful feedback on an earlier version of this paper. The two issues discussed in Sect. 5 were first raised by Vignero and Termont, respectively. The ideas presented in this paper were first proposed in one of the additional theses of my PhD dissertation (Demey 2014). My research is financially supported by a Postdoctoral Fellowship of the Research Foundation–Flanders (FWO).
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Demey, L. The Porphyrian Tree and Multiple Inheritance: A Rejoinder to Tylman on Computer Science and Philosophy. Found Sci 23, 173–180 (2018). https://doi.org/10.1007/s10699-017-9531-1
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DOI: https://doi.org/10.1007/s10699-017-9531-1