There is, I should think, little doubt that if, in a case of the kind under consideration, a jury found that a plaintiff had been negligent or careless in some respect they would not find against him on an issue of contributory negligence if they were of opinion that his negligence was "not sufficiently important and closely connected with the accident to make it reasonable on a broad commonsense view to regard its author as responsible for it" or "so remote from the accident or so trifling in its effect that commonsense would reject it as a ground for liability". It may, perhaps, safely be said that if the plaintiff's negligence was so remote or trivial that a broad commonsense approach to the problem would require its rejection as a ground of liability no reasonable jury would be likely to regard it as a cause of the accident. But the adoption of the words "substantial" or "material" to make the duty of the jury clear in this respect is open to question for those words, in cases of this type, may well be taken to exclude a wider category of negligent acts than those which may fairly be said to be remote or trivial in the sense already mentioned. The word "substantial" may be understood to exclude negligence which is neither remote nor trivial in that sense, whilst the word "material" does not, of itself, provide a test at all and merely avoids the necessity of saying what is and what is not material negligence. The words were, of course, used by Lord Wright for a particular purpose in Caswell v Powell Duffryn Associated Collieries [1] where, in speaking of the facts of that case, he said: - "If the defendants' negligence or breach of duty is established as causing the death, the onus is on the defendants to establish that the plaintiff's contributory negligence was a substantial or material co-operating cause" [2] . It is clear that his Lordship, in using the words "substantial" and "material" had in mind that inadvertence and thoughtlessness is of necessity a common and persistent feature of work in industrial occupations and he sought to distinguish between acts or omissions emanating from these sources - and in respect of which it was a purpose of the relevant statutory requirements to make provision - and acts of negligence which themselves constitute either the sole or a contributing cause of an injury to a workman. That this is so is clear from his Lordship's observations that: "The circumstances under which men working in a mine or a factory are exposed to risk when machinery is unfenced in breach of statutory duty have general characteristics of their own. These have to be carefully considered when the question is whether a man was negligent. I think the importance of the ruling of Lawrence J. is that he drew attention to these general conditions of work and thereby gave a good practical direction and definition to help in deciding the issue of fact in any particular case. The learned judge did not mean that there are grades or degrees of negligence or that the plaintiff is not prevented from recovering by "mild" negligence but only by "gross" negligence. Generally speaking in civil cases "gross" negligence has no more effect than negligence without an opprobrious epithet. Negligence is the breach of that duty to take care, which the law requires, either in regard to another's person or his property, or where contributory negligence is in question, of the man's own person or property. The degree of want of care which constitutes negligence must vary with the circumstances. What that degree is, is a question for the jury or the Court in lieu of a jury. It is not a matter of uniform standard. It may vary according to the circumstances from man to man, from place to place, from time to time. It may vary even in the case of the same man. Thus a surgeon doing an emergency operation on a cottage table with the light of a candle might not properly be held guilty of negligence in respect of an act or omission which would be negligence if he were performing the same operation with all the advantages of the serene atmosphere of his operating theatre; the same holds good of the workman. It must be a question of degree. The jury have to draw the line where mere thoughtlessness or inadvertence or forgetfulness ceases and where negligence begins" [1] . There is nothing in his Lordship's reasons to suggest that if it be shown that a plaintiff's negligence was an effective cause of his injuries it can in any circumstances be disregarded merely because it was negligence of a minor degree or, as his Lordship said, merely "mild" and not "gross" negligence. On the contrary his Lordship was clearly of the opinion that the issue of contributory negligence must be found against a plaintiff if negligence on his part is established and it is shown that that negligence was an effective cause of his injuries. Lord Atkin, with whom Lord Macmillan agreed, found it impossible to divorce any theory of contributory negligence from the concept of causation. After so expressing himself his Lordship went on: "It is negligence which "contributes to cause" the injury, a phrase which I take from the opinion of Lord Penzance in Radley v London & North Western Rly. Co. [2] . And whether you ask whose negligence was responsible for the injury, or from whose negligence did the injury result, or adopt any other phrase you please, you must in the ultimate analysis be asking who "caused" the injury; and you must not be deterred because the word "cause" has in philosophy given rise to embarrassments which in this connection should not affect the judge" [3] .