From the time of Alfred to the present day, statutes and decisions have busied themselves with defining the precautions to be taken in certain familiar cases; that is, with substituting for the vague test of the care exercised by a prudent man, a precise one of specific acts or omissions.  The fundamental thought is still the same, that the way prescribed is that in which prudent men are in the habit of acting, or else is one laid down for cases where prudent men might otherwise be in doubt.

It will be observed that the existence of the external tests of liability which will be mentioned, while it illustrates the tendency of the law of tort to become more and more concrete by judicial decision and by statute, does not interfere with the general doctrine maintained as to the grounds of liability.  The argument of this Lecture, although opposed to the doctrine that a man acts or exerts force at his peril, is by no means opposed to the doctrine that he does certain particular acts at his peril.  It is the coarseness, not the nature, of the standard which is objected to.  If, when the question of the defendant’s negligence is left to a jury, negligence does not mean the actual state of the defendant’s mind, but a failure to act as a prudent man of average intelligence would have done, he is required to conform to an objective standard at his [113] peril, even in that case.  When a more exact and specific rule has been arrived at, he must obey that rule at his peril to the same extent.  But, further, if the law is wholly a standard of external conduct, a man must always comply with that standard at his peril.

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