Identity - Identity, Persistence, and the Ship of Theseus...

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Identity, Persistence, and the Ship of Theseus Heraclitus’s “river fragments” raise puzzles about identity and persistence: under what conditions does an object persist through time as one and the same object? If the world contains things which endure, and retain their identity in spite of undergoing alteration, then somehow those things must persist through changes . Heraclitus wonders whether one can step into the same river twice precisely because it continually undergoes changes. In particular, it changes compositionally . At any given time, it is made up of different component parts from the ones it was previously made up of. So, according to one interpretation, Heraclitus concludes that we do not have (numerically) the same river persisting from one moment to the next. Plato is probably the source of this “paradoxical” interpretation of Herclitus. According to Plato, Heraclitus maintains that nothing retains its identity for any time at all: “Heraclitus, you know, says that everything moves on and that nothing is at rest; and, comparing existing things to the flow of a river, he says that you could not step into the same river twice” ( Cratylus 402A). But what Heraclitus actually said was more likely to have been this: “On those who enter the same rivers, ever different waters flow.” (fr. 12) On Plato’s interpretation, it’s not the same river, since the waters are different. On a less paradoxical interpretation, it is the same river, in spite of the fact that the waters are different. On both interpretations of Heraclitus, he holds the Flux Doctrine : Everything is constantly altering; no object retains all of its component parts from one moment to the next. The issue is: what does Flux entail about identity and persistence? Plato’s interpretation requires that Heraclitus held what might be called the Mereological Theory of Identity ( MTI ), i.e., the view that the identity of an object depends on the identity of its component parts. This view can be formulated more precisely as follows: For any compound objects, x and y , x = y only if every part of x is a part of y , and every part of y is a part of x . I.e., an object continues to exist (from time t 1 to time t 2 ) only if it is composed of all the same components at t 2 as it was composed of at t 1 . Sameness of parts is a necessary condition of identity. It now seems that if we want to allow that an object can persist through time in spite of a change
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This note was uploaded on 11/26/2011 for the course PHILOSOPHY 101 taught by Professor Buechner during the Fall '06 term at Rutgers.

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Identity - Identity, Persistence, and the Ship of Theseus...

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