Logic: A Very Short Introduction by Graham Priest

Author:Graham Priest
Language: eng
Format: epub, pdf
ISBN: 9780192539700
Publisher: OUP Oxford
Published: 2017-08-21T04:00:00+00:00

Main ideas of the chapter

• is true just if the names m and n refer to the same object.

• If two objects are the same, any property of one is a property of the other (Leibniz’s Law).

Chapter 10

Vagueness: how do you stop sliding down a slippery slope?

While we are on the subject of identity, here is another problem about it. Everything wears out in time. Sometimes, parts get replaced. Motor bikes and cars get new clutches; houses get new roofs; and even the individual cells in people’s bodies are replaced over time. Changes like this do not affect the identity of the object in question. When I replace the clutch on my bike, it remains the same bike. Now suppose that over a period of a few years, I replace every part of the bike, Black Thunder. Being a careful fellow, I keep all the old parts. When everything has been replaced, I put all the old parts back together to recreate the original bike. But I started off with Black Thunder; and changing one part on a bike does not affect its identity: it is still the same bike. So at each replacement, the machine is still Black Thunder; until, at the end, it is—Black Thunder. But we know that that can’t be right. Black Thunder now stands next to it in the garage (Figure 10).

10. A bike-rider’s dilemma.

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