L’accident est une défense relative à la mens rea, mais aussi relative à l’actus reus
 There is no question that accident is a good defence to the element of intention in murder or to any other offence in which a culpable mental state is an essential element. Accidents are, by definition, not intentional. An accident is not the result of a deliberate choice to engage in specific conduct or to cause a specific result. To the extent that the criminal law allows liability to be found in the absence of such choice it condones constructive liability because it allows responsibility to be attributed in the absence of an essential element. But accident is not only a defence to an element of mens rea. Accident is also a defence to the actus reus of an offence. What is common between them is that both, but for distinct reasons, preclude proof beyond reasonable doubt of essential elements of an offence.
 For an act to be attributed to the responsibility of a person in the criminal law it must be voluntary. Accidents are, by definition, not voluntary. A voluntary act is the expression of a conscious choice and conscious control by the person who commits it. To this extent the actus reus of an offence includes a mental element. This mental element merges with elements of mens rea but must be distinguished from them. The mental element in the voluntariness, or conscious choice, merges with elements of mens rea in the sense that elements such as intention, knowledge, wilful blindness and recklessness presuppose the exercise of conscious choice. They cannot exist except upon a foundation of conscious choice. What distinguishes the element of conscious choice in the actus reus from the mental element in mens rea is that states of mind such as intention, knowledge, wilful blindness and recklessness define particular types of conscious choice. In addition to proof of a voluntary act the proof of such elements, as required by the substantive law in the definition of specific offences, justifies a verdict that a person is guilty for a conscious choice in the commission of a prohibited act.
 Accident negates the element of conscious choice, or voluntariness, in action as much as it negates specific types of choices as defined in various concepts of mens rea. Thus a driver who unavoidably strikes a pedestrian who streaks into the road cannot be held criminally responsible for voluntary conduct or fault in the commission of an offence.
 An accident that occurs in the absence of any other unlawful act precludes any criminal liability. This is not a complicated proposition. But the criminal law must also account for accidents that are caused by previously committed offences or accidents that occur during the commission of an unlawful act. The present case concerns the second issue. The theory of the defence was that during (not after) the commission of an assault the gun accidentally discharged and the shot killed the victim.
 Assuming a sufficient factual foundation in the evidence, this theory forces consideration of the extent to which criminal responsibility can be attributed where accidents occur during the commission of other offences. This possibility has been rejected to the extent that constructive murder, a killing in the absence of subjective foresight of death, has been declared unconstitutional. It has not been rejected with respect to other offences, including other forms of culpable homicide. Unlawful-act manslaughter allows for conviction where an accidental death is caused by the commission of an underlying or predicate offence, such as assault, if the commission of that offence is dangerous in the sense that it demonstrates an objective risk of bodily harm.
 As a general proposition, for which exceptions are not involved in this appeal, there can be no liability for first-degree murder unless the commission of an underlying offence is the cause of death; nor will it suffice that a person caused death while committing an underlying offence. Murder requires subjective foresight of death in the act of killing. It is clear that the judge instructed the jury to consider the defence of accident in relation to the element of intention in section 229(a) of the Code. He made no reference to accident in relation to the actus reus of murder or manslaughter, nor any mention of the elements of unlawful-act manslaughter.
 If the instructions had included a direction on accident with respect to the actus reus, the jury would have had a clearer understanding between the possible verdicts of murder or unlawful-act manslaughter. If as a result of such an instruction the jury had a reasonable doubt concerning the voluntariness of the shot, and thus of causation, the only alternative verdict would be manslaughter by means of an unlawful act. The absence of an instruction concerning accident and the actus reus implied that the only defence to a charge of murder would be reasonable doubt on the element of intention defined in section 229(a). It did not account for the possibility that there was a defence of accident if the discharge of the gun was not an act that was voluntary or the expression of a conscious choice.