Written Reflection

Ship of Theseus Puzzle

The Ship of Theseus

• This is a puzzle that has been around since antiquity, probably later than Heraclitus, but not much later.

The Ship of Theseus

• The original puzzle is this: over the years, the Athenians replaced each plank in the original ship of Theseus as it decayed, thereby keeping it in good repair

The Ship of Theseus

• Eventually, there was not a single plank left of the original ship. So, did the Athenians still have one and the same ship that used to belong to Theseus?

The Ship of Theseus

• Let us consider two new versions of the puzzle. On both versions, the replacing of the planks takes place while the ship is at sea.

The Ship of Theseus

• We are to imagine that Theseus sails away, and then systematically replaces each plank on board with a new one. (He carries a complete supply of new parts on board as his cargo.)

The Ship of Theseus

• Simple version: Theseus completely rebuilds his ship, replaces all the parts, throws the old ones overboard. Does he arrive on the same ship as the one he left on? Of course it has changed. But is it it?

Two Theories of Identity

• Mereological Theory of Identity (MTI)- An object is the same at two times iff it has all of the same parts.

• Problem: Theseus changed ships during his voyage.

Two Theories of Identity

• Spatio-temporal continuity theory of identity (STC)- a persisting object must trace a continuous path through space-time.

• Problem: shipping my bicycle.

The Ship of Theseus

• Complex version: Like the simple version, but with one addition -- following Theseus in another boat is the Scavenger, who picks up the pieces Theseus throws overboard, and uses them to rebuild his boat.

The Ship of Theseus

• Complex version: The Scavenger arrives in port in a ship composed of precisely the parts that composed the ship Theseus started out in. He docks his ship right next to one that Theseus docked.