Abstract

It is often said that impenetrability is the mark of the material, and that whatever is real is material. This naive materialism however faces many putative counterexamples: 1. a tree and the molecules that compose it (Wiggins, 1968): they are distinct (the tree can survive the loss of some molecules, the molecules can survive the death of the tree) and both are at the same place at the same time. 2. Tibbles-minus-tail and Tib (Wiggins, 1968): At t1, Tibbles is a cat and Tib a proper part of it which corresponds to Tibbles without its tail. Tibbles and Tib are distinct. At t2, Tibble loses its tail. Then at t2, both Tibbles and Tib are in the same place at the same time