"... of all crimes manslaughter appears to afford most difficulties of definition, for it concerns homicide in so many and so varying conditions. From the early days when any homicide involved penalty the law has gradually evolved 'through successive differentiations and integrations' until it recognizes murder on the one hand, based mainly, though not exclusively, on an intention to kill, and manslaughter on the other hand, based mainly, though not exclusively, on the absence of intention to kill but with the presence of an element of 'unlawfulness' which is the elusive factor. In the present case it is only necessary to consider manslaughter from the point of view of an unintentional killing caused by negligence, that is, the omission of a duty to take care. I do not propose to discuss the development of this branch of the subject as treated in the successive treatises of Coke, Hale, Foster and East and in the judgments of the Courts to be found either in directions to juries by individual judges or in the more considered pronouncements of the body of judges which preceded the formal Court of Crown Cases Reserved. Expressions will be found which indicate that to cause death by any lack of due care will amount to manslaughter; but as manners softened and the law became more humane a narrower criterion appeared. After all, manslaughter is a felony, and was capital, and men shrank from attaching the serious consequences of a conviction for felony to results produced by mere inadvertence. The stricter view became apparent in prosecutions of medical men or men who professed medical or surgical skill for manslaughter by reason of negligence. As an instance I will cite Rex v Williamson [1807] EngR 87; (1807) 3 C & P 635 where a man who practised as an accoucheur, owing to a mistake in his observation of the actual symptoms, inflicted on a patient terrible injuries from which she died. 'To substantiate that charge' - namely, manslaughter - Lord Ellenborough said, 'the prisoner must have been guilty of criminal misconduct, arising either from the grossest ignorance or the most criminal inattention.' The word 'criminal' in any attempt to define a crime is perhaps not the most helpful: but it is plain that the Lord Chief Justice meant to indicate to the jury a high degree of negligence. So at a much later date in Rex v Bateman 19 Cr App R 8 a charge of manslaughter was made against a qualified medical practitioner in similar circumstances to those of Williamson's case [1807] EngR 87; (1807) 3 C & P 635. In a considered judgment of the Court the Lord Chief Justice, after pointing out that in a civil case once negligence is proved the degree of negligence is irrelevant, said 19 Cr App R 11, 'In a criminal Court, on the contrary, the amount and degree of negligence are the determining question. There must be mens rea.' After citing Cashill v Wright [1856] EngR 744; (1856) 6 E & B 891, a civil case, the Lord Chief Justice proceeds 'In explaining to juries the test which they should apply to determine whether the negligence, in the particular case, amounted or did not amount to a crime, judges have used many epithets such as "culpable," "criminal," "gross," "wicked," "clear," "complete." But whatever epithet be used and whether an epithet be used or not, in order to establish criminal liability the facts must be such that, in the opinion of the jury, the negligence of the accused went beyond a mere matter of compensation between subjects and showed such disregard for the life and safety of others as to amount to a crime against the State and conduct deserving punishment.' Here again I think with respect that the expressions used are not, indeed they probably were not intended to be, a precise definition of the crime. I do not myself find the connotations of mens rea helpful in distinguishing between degrees of negligence, nor do the ideas of crime and punishment in themselves carry a jury much further in deciding whether in a particular case the degree of negligence shown is a crime and deserves punishment. But the substance of the judgment is most valuable, and in my opinion is correct. In practice it has generally been adopted by judges in charging juries in all cases of manslaughter by negligence, whether in driving vehicles or otherwise. The principle to be observed is that cases of manslaughter in driving motor cars are but instances of a general rule applicable to all charges of homicide by negligence. Simple lack of care such as will constitute civil liability is not enough: for purposes of the criminal law there are degrees of negligence: and a very high degree of negligence is required to be proved before the felony is established. Probably of all the epithets that can be applied 'reckless' most nearly covers the case. It is difficult to visualize a case of death caused by reckless driving in the connotation of that term in ordinary speech which would not justify a conviction for manslaughter: but it is probably not all-embracing, for 'reckless' suggests an indifference to risk whereas the accused may have appreciated the risk and intended to avoid it and yet shown such a high degree of negligence in the means adopted to avoid the risk as would justify a conviction. If the principle of Bateman's case 19 Cr App R 8 is observed it will appear that the law of manslaughter has not changed by the introduction of motor vehicles on the road. Death caused by their negligent driving, though unhappily much more frequent, is to be treated in law as death caused by any other form of negligence: and juries should be directed accordingly."