Section 2.01 of Model Penal Code sets out Code's version of notoriously difficult or requirement of an actus reus. A number of philosophers of law have commented upon confusion which surrounds notion of an act as a requirement for criminal liability. Hyman Gross holds that ...acts are not bodily movements. Those who talk as though they were do not reflect common sense, but simply resolve summarily by fiat an important problem that all of us in a more thoughtful moment perceive as difficult and obscure.[1] Later he tells us that the act itself, or rather very idea of an act, still remains veiled in mystery.[2] Glanville Williams has also stated: Considerable confusion reigns, both in ordinary speech and in legal speech, on what is meant by an act.[3] And D. O'Connor has added that the thoroughgoing analysis of actus reus necessary for criminal liability has yet to arrive,[4] a claim that Douglas Husak cites with approval and agreement.[5] Problems Stemming From Act Requirement This issue is not merely a definitional one. There are several traditional legal problems surrounding act requirement. One involves omissions. If an affirmative act is paradigm for criminal liability, how can one be liable for not acting? A standard account of an act for purposes of act requirement in criminal law is that it be a muscular contraction. This is John Austin's[6] account, as it is Holmes's[7] and J.S. MNill,s.[8] This view of a criminal act has been roundly criticized by H.L.A. Hart, among others.[9] Hart's criticism turns on two points, one of which is precisely ours.[10] Omissions are not muscular contractions of any sort, willed or otherwise. In this sense, they are non-events. Hart tells us...it is absurd even to attempt to fit omissions into such a picture....[11] A broader, but essentially simpler, definition is exemplified by Model Penal Code (hereinafter Code), where wer are told 'act' or 'action' means a bodily movement whether voluntary or involuntary.[12] But this definition is faulted by Meir Dan Cohen precisely because it fails to include omissions (as well as possession).[13] A second, even more serious, problem is posed by negligence and strict liability. So-called involuntary actions, such as muscle spasms or movements while unconscious, must be excluded if act requirement is to mean anything. And they are excluded in Code.[14] Yet, unintentional action must be able to create liability in cases of negligence or strict liability, without throwing out act requirement. That is, if I negligently run over an infant in my car, it fails to be murder precisely because killing, indeed collision, was unintentional. How is this different from an involuntary act? The acts of driving, colliding, and killing are mine, and, based on a negligence doctrine, I can be held liable for them. But I cannot be held responsible if I lapse into unconsciousness at wheel (so long as it is not through earlier fault of my own). Intuitively, we sense a difference between an unintentional and an involuntary act, but how can we explain it? In neither case was I guilty of performing act of intentionally running over someone. What is conceptual difference between unintentionally driving over an infant and behavior of unconsciously doing so? And why should that conceptual difference make a moral and legal difference? In a way similar to negligence, but totally dissimilar to involuntary acts, actions giving rise to strict liability are unintentional. If I am liable, under a strict liability statute, for harm done to persons by my explosive demolition work, it is assumed that harm was unintentional, lest it be battery or murder, that is, an intentional wrong. Yet, I am responsible for effects of demolition, that is, of effects of my act. …