“…[aside from some metaphysicians] I may venture to affirm of the rest of mankind, that they are nothing but a bundle or collection of different perceptions, which succeed each other with an inconceivable rapidity, and are in a perpetual flux and movement… the mind is a kind of theatre, where several perceptions successively make their appearance… there is properly no simplicity in it at one time, nor identity in different, whatever natural propension we may have to imagine that simplicity and identity.” – David Hume, Treatise

Theseus’ ship is dismantled to get it through a narrow channel. Plank by plank, the ship is dis-assembled and reassembled after the parts are carried a short distance. Is the re-constituted ship now Theseus’ ship?

As pieces rot or break, these planks are replaced. After several years, none of the original planks remain. Through these changes, does it remain Theseus’ ship?

Suppose now, that as a variation on the second scenario, the replaced planks are not broken or rotted. (Perhaps Theseus wanted to change his oaken ship into a maple one, and couldn’t afford the transformation all at once.) Suppose further that now the discarded (oak) planks are re-assembled. So after these changes, there’s both the oak ship and the maple one. Question: which is Theseus’ ship?

X = Y (they are numerically identical) if and only X and Y have all of their properties in common. (X has no property Y lacks and vice versa.)

There is no permanent self. In favor: Essentially dissolves distinction between q.i. and n.i. – appealing in its simplicity. Against: At odds with the way we think about persons: -e.g. practical (savings, planning) -identification

People are identical with their bodies. In favor: Makes us of a piece with animals and their identity. Works with vegetative state cases (it seems). Against: Implies that living on in another body is incoherent. (life after death; radical body transplant)

UQ, The Illusion and Body Theories, pp. 110 – Food for Thought, p Food for Thought, p. 114.