Full Idea
Some individuals to gain or lose certain capacities or powers, but do not thereby lose their identity. They still have the same nature. A drug, or photographic paper, may lose effectiveness over time.
Gist of Idea
Some individuals can gain or lose capacities or powers, without losing their identity
Source
Harré,R./Madden,E.H. (Causal Powers [1975], 1.II.C)
Book Reference
Harré,R/Madden,E.H.: 'Causal Powers: A Theory of Natural Necessity' [Blackwell 1975], p.14
A Reaction
Damn! I thought I was the first to spot this problem! I, however, take it to be much more metaphysically significant than Harré and Madden do. The question is whether those properties were essential, since they can be lost. Essential but not necessary!