Introduction

The Irresistible Impulse Test

Introduction

Criminal law excuses a mentally ill defendant on the premise that punishment is deserved only by a person who was capable of choosing to obey the law. A test that measures that capacity by cognition alone asks whether the defendant knew the nature of the act or knew that it was wrong. That question catches the defendant whose illness distorted perception or understanding. It says nothing about a defendant who can recite that the act is a crime, who understands exactly what the act will do, and who still cannot hold himself back. Such a person passes the knowledge inquiry and is convicted, even though the illness removed the very capacity that makes blame fair. The control inquiry exists to close that gap.

The traditional rule is stated in terms of that missing capacity. Under the irresistible impulse test, a defendant is entitled to an acquittal if, as a result of mental illness, the defendant could not control his actions or could not conform his conduct to the requirements of the law.¹ Courts and commentators also call it the control test or the volitional test, names that identify the faculty at issue, which is the defendant's volition.² The jurisdictions that have adopted it have generally combined it with the M'Naghten rules, so it works as a second route to acquittal added to the knowledge inquiry, which remains in place.³ The label "impulse" suggests a sudden urge, yet the lack of control may develop or exist over time, a point the discussion of elements takes up in detail.⁴

This chapter follows the order in which the doctrine developed. It begins with the history of the control inquiry, then separates the test into its parts and sets it beside a jurisdiction that asks only about right and wrong. From there it turns to how loss of control is proved before a jury, to the question whether the Constitution requires any state to adopt the test, and finally to the criticisms that led courts and drafters to look past it for broader formulations. The first step is the history: how courts that had long asked only what a defendant knew came to ask what the defendant could control.