An Analysis of Persistence

Abstract

‘Something persists iff it exists at more than one time’ asserts Lewis. How things persist takes two forms: ‘something perdures iff it persists by having different temporal parts, or stages, at different times’ whereas ‘it endures iff it persists by being wholly present at more than one time. Lewis’ words show insight although some of their import has been overlooked. The debate has been articulated mainly around the interplay between theories of time and persistence, oblivious of the evidence that Lewis’ definitions embed philosophically ubiquitous and crucial notions like existence (and identity) which deserves to be investigated. In addition, the inquiry has often moved from time to persistence: e.g. teasing out the features that a specific view of time had which yielded a specific theory of persistence, whereas as it has recently been urged the relationship between views of time and persistence might be more relaxed: any theory of time could fit with any theory of persistence.
This thesis is an exploration of persistence, time, and existence (and to a lesser extent identity) to make sense of whether and how the first could affect the others. The investigation is restricted to material objects (though little depends upon this), and to how and why the intuitions and common sense considerations in the background of perdurance, the theory of persistence I sympathise with, motivate a specific theory of time, i.e. eternalism; and finally how both afford a specific notion of existence, to wit a view of existence a là Quine, according to which existence is delimited by true uses of the existential quantifier. Thus, the direction of investigation will be from persistence, via time, to existence. The reason for this is that change is an undeniable datum of experience for which we have robust intuitions and common sense considerations, whilst time, although pervasive, is so in an elusive way which is hard to pin down.
The thesis is divided into three parts which mirror the three main topics spelt out above. In the first part, a case of a persisting object will be used to show that our common sense thinking and intuitions harbour a predicament: it appears plausible to believe that there is a fact of the matter whether an object is or is not one and the same although we may not be able pin down the reason why. This will be clarified without supposing these intuitions and common sense considerations to be inviolable. The focus will be on two main contenders, perdurance and endurance, and what discriminates between them: the notion of temporal parts. Their centrality makes it decisive to understand what temporal parts are and what they do. It will be argued that whilst the debate has reached a stalemate in attempting to define temporal parts, the notion rests upon a robust basis of intuitions and common sense considerations which draw upon our ordinary understanding of parts in space, and this is sufficient to give a working grasp of them as well as the potential for a definition which stands scrutiny. It has also been argued that temporal parts are decisive in solving some puzzling situations; therefore I will examine one of these, the long-standing problem of change, and show that there is a sense in which it might not be a genuine metaphysical problem. Leibniz’s Law is a law of logic and it is best formulated accordingly; whereas the way it is used to generate the problem of change is metaphysically loaded. The problem of change as a metaphysical problem is thus deflated but, it will be argued, there are better, more intuitive, ways of motivating perdurance.
The intelligibility and possibility of temporal parts, and hence perdurantism, has been shown to rely on the thought that reality is four-dimensional, so that in addition to the three spatial dimensions in which reality uncontentiously extends, there is a fourth, time, along which similarly reality extends. In the second part I shall consider if what philosophers have said about this stands scrutiny. Philosophers have argued that space and time share some decisive features (the similarity thesis); it might be hoped that investigating what they have said will clarify whether and how time could be so considered. I will argue that such an investigation will leave the space/time analogy wanting, and therefore I shall endeavour to venture a tentative picture of time which could accommodate the similarity thesis as well as a view of time as extended. I will then take a brief look into the current debate in the philosophy of time and tease out what the different theories of time are really about, their basic assumptions which are supposed to make manifest how each view sees time and what they try to defend as basic features of it. I will make clear why perdurance’s four-dimensional view of reality is most appealing if combined with an eternalist view of time according to which every time co-exists; both four-dimensionalism and eternalism sharing the assumption that time is a dimension through which things extend.
In the third part, I unveil the nexus between perdurance, eternalism, and the notion of existence. I argue that perdurance’s basic assumption that reality is four-dimensional which is shared by eternalism, motivates a view of existence a là Quine, since it guarantees an existentially closed domain of existents, which is what perdurance and eternalism imply. The overall conclusion is that once unpacked, perdurance, eternalism, and a view of existence a là Quine fit together in a way in which each one motivates the others. Each has intuitions and assumptions that it tries to preserve and defend; intuitions and assumptions which might not be preserved if the theories are combined differently.