From Spiva v. Astrue (7th Cir. December 6, 2010)
The government implies that if the administrative law judge’s opinion consisted of two words—“benefits denied”—a persuasive brief could substitute for the missing opinion. That is incorrect. It would displace the responsibility that Congress has delegated to the Social Security Administration—the responsibility not merely to gesture thumbs up or thumbs down but to articulate reasoned grounds of decision based on legislative policy and administrative regulation—into the Justice Department, which represents the agency in the courts.
Update: Just to clarify: The Administrative Law Judge (ALJ) decision did not consist merely of two words. The Court of Appeals found the ALJ's rationale sorely lacking and held that Social Security could not defend the decision by telling the Court what rationale the ALJ could have used. The Court held that the ALJ decision must be judged upon what it said, not upon what it might have said.