Some examples of the process of specification will be useful. In LL. Alfred, 36, /1/ providing for the case of a man's staking himself on a spear carried by another, we read, "Let this (liability) be if the point be three fingers higher than the hindmost part of the shaft; if they be both on a level,... be that without danger." The rule of the road and the sailing rules adopted by Congress from England are modern examples of such statutes. By the former rule, the question has been narrowed from the vague one, Was the party negligent? to the precise one, Was he on the right or left of the road? To avoid a possible misconception, it may be observed that, of course, this question does not necessarily and under all circumstances decide that of liability; a plaintiff may have been on the wrong side of the road, as he may have been negligent, and yet the conduct of the defendant may have been unjustifiable, and a ground of liability. /2/ So, no doubt, a defendant could justify or excuse being on the wrong side, under some circumstances. The difference between alleging that a defendant was on the wrong side of the road, and that he was negligent, is the difference between an allegation of facts requiring to be excused by a counter allegation of further facts to prevent their being a ground of liability, and an allegation which involves a conclusion of law, and denies in advance the existence of an [114] excuse. Whether the former allegation ought not to be enough, and whether the establishment of the fact ought not to shift the burden of proof, are questions which belong to the theory of pleading and evidence, and could be answered either way consistently with analogy. I should have no difficulty in saying that the allegation of facts which are ordinarily a ground of liability, and which would be so unless excused, ought to be sufficient. But the forms of the law, especially the forms of pleading, do not change with every change of its substance, and a prudent lawyer would use the broader and safer phrase.