 Recall that SD—exponential divergence of neighboring trajectories—is taken by many to be a necessary condition for chaos. As we saw in  §3,  it is not straightforward to confirm when we have a model serving as a good explanation because, for instance, the slightest refinement of initial conditions can lead to wildly differing behavior. So on many standard approaches to confirmation and models, it would be difficult to say when we had a good explanation. Even if we push the faithful model assumption to its extreme limit—i.e., assuming the model is perfect—we run into tricky questions regarding confirmation since there are too many states indistinguishable from the actual state of the system yielding empirically indistinguishable trajectories in the model state space (Judd and Smith 2001). 