The depth of the assumption in law that brains cause minds can be seen in the subtle way the court in Heller v. Doe, 509 U.S. 312 (1993) decided on the standard of proof that should be required in different mental health situations.

The case involved the standard of proof in involuntary commitment proceedings. The court had applied the clear and convincing standard (more stringent than the preponderance standard, but less than beyond reasonable doubt) to determine whether the person was mentally ill. The court held that that was a mistake. Clear and convincing is proper, the court held, in mental retardation cases, where the underlying biology is well known and easier to prove, but in mental illness the brain/mind picture is not nearly so clear, so it should be subject to the stricter standard.

The Heller court's conclusion is based on a standard piece of legal epistemology: The harder it is to understand something, the higher the standard of proof required. The court reveals a clear sense of the brain/mind situation and the epistemological uncertainty it presents.