Single Idea 9655

[catalogued under 8. Modes of Existence / B. Properties / 11. Properties as Sets]

Full Idea

We can't take a property as sets of this-worldly instances, because two properties may be coextensive. Some say it is just as bad in all possible worlds, if the property is necessary, as when all triangles are trilateral, which seem different.

Gist of Idea

Trilateral and triangular seem to be coextensive sets in all possible worlds


David Lewis (On the Plurality of Worlds [1986], 1.5)

Book Reference

Lewis,David: 'On the Plurality of Worlds' [Blackwell 2001], p.55

A Reaction

[compressed] Renate/cordate is the standard example of the first problem. Lewis seems to equivocate over exactly what is meant by a property. I take the example to be a powerful objection to treating properties as sets.