The doctrine advocated by David Lewis, that different possible worlds are to be thought of as existing exactly as this one does. Thinking in terms of possibilities is thinking of real worlds where things are different. The view has been charged with making it impossible to see why it is good to save the child from drowning, since there is still a possible world in which she (or her counterpart) drowned, and from the standpoint of the universe it should make no difference which world is actual. Critics also charge either that the notion fails to fit with a coherent theory of how we know about possible worlds, or with a coherent theory of why we are interested in them, but Lewis denied that any other way of interpreting modal statements is tenable.