concurring:
I join the majority opinion and write briefly only to confirm my understanding of our disposition. On remand, the parties should be guided by the following principal points:
First, the District Court erred insofar as it held that no bipolar disorder can be a “mental illness” as defined in the Unum policy. Even counsel for Fitts recognized that some disorders can be accurately characterized as mental illnesses under the policy — if not, the provision in question would be rendered meaningless. Because the phrase “bipolar disorder” covers a range of cases, some of which may be mental illnesses and some which may not, whether a person’s disorder can be characterized as “bipolar” is not, by itself, dispos-itive. To the extent that the District Court held that bipolar disorder is never a mental illness, its conclusion was wrong as a matter of law.
Second, if Fitts’ bipolar disorder did not have a physical cause, appellees have presented no argument that it is not a “mental illness,” and therefore it falls within Unum’s policy limitation. The facts con*503cerning the cause of Fitts’ disorder were disputed, however, so summary judgment on this point was inappropriate. The District Court never settled the question of whether Fitts’ disorder had physical causes. Because Fitts offers no viable argument that a non-physically caused bipolar disorder is not a mental illness, the resolution of this factual question may dispose of this case on remand.
Third, it is unclear whether Fitts’ bipolar disorder can be properly characterized as a “mental illness” if it has been caused in part by physical factors. Unum admits that some neurological disorders with physical causes and behavioral symptoms — such as Alzheimer’s disease or vascular dementia — are not mental illnesses as defined by its policy. If it is determined that Fitts’ bipolar disorder does have a physical cause, then, at the very least, the District Court must determine whether the causal nexus between physical factors and behavior symptoms for Fitts’ bipolar disorder are more similar to the neurological disorders fully covered by Unum, or to traditional mental illnesses that are subject to the policy limitation. The evidence on this point is disputed, so summary judgment is inappropriate.