Mine is: "I am sitting with a philosopher in the garden; he says again and again 'I know that that's a tree,' pointing to a tree that is near us. Someone else a

Mine is: "I am sitting with a philosopher in the garden; he says again and again 'I know that that's a tree,' pointing to a tree that is near us. Someone else arrives and hears this, and I tell them: 'This fellow isn't insane. We are only doing philosophy.'"