“But supposing B brings the bolt, as in 14c), & on comparing it with the pattern it turns out to be the wrong one?” ‒ ‒ But couldn't that have happened in all the other cases as well? Suppose in 14a) the bolt which B brought back was found not to match with the pattern. Wouldn't we in some such cases say that his memory image had changed, in others that the pattern or the material had changed, in others again that the light had changed? It is not difficult to invent cases, imagine circumstances, in which each of these judgements would be made. ‒ ‒ “But isn't there after all an essential difference between the cases 14a) & 14c)?‒ ‒ Certainly! Just that pointed out in the description of these cases. ‒ ‒