ing； that the facts in evidence are all the facts。
The cases which have raised difficulties needing explanation are those in which the court has ruled that there was prima facie evidence of negligence； or some evidence of negligence to go to the jury。
Many have noticed the confusion of thought implied in speaking of such cases as presenting mixed questions of law and fact。 No doubt； as has been said above； the averment that the defendant has been guilty of negligence is a complex one： first； that he has done or omitted certain things； second； that his alleged conduct does not come up to the legal standard。 And so long as the controversy is simply on the first half； the whole complex averment is plain matter for the jury without special instructions； just as a question of ownership would be where the only dispute was as to the fact upon which the legal conclusion was founded。 /1/ But when a controversy arises on the second half； the question whether the court or the jury ought to judge of the defendant's conduct is wholly unaffected by the accident； whether there is or is not also a dispute as to what that conduct was。 If there is such a dispute； it is entirely possible to give a series of hypothetical instructions adapted to every state of facts which it is open to the jury to find。 If there is no such dispute； the court may still take their opinion as to the standard。 The problem is ＇123＇ to explain the relative functions of court and jury with regard to the latter。
When a case arises in which the standard of conduct； pure and simple； is submitted to the jury； the explanation is plain。 It is that the court； not entertaining any clear views of public policy applicable to the matter； derives the rule to be applied from daily experience； as it has been agreed that the great body of the law of tort has been derived。 But the court further feels that it is not itself possessed of sufficient practical experience to lay down the rule intelligently。 It conceives that twelve men taken from the practical part of the community can aid its judgment。 /1/ Therefore it aids its conscience by taking the opinion of the jury。
But supposing a state of facts often repeated in practice； is it to be imagined that the court is to go on leaving the standard to the jury forever？ Is it not manifest； on the contrary； that if the jury is； on the whole； as fair a tribunal as it is represented to be； the lesson which can be got from that source will be learned？ Either the court will find that the fair teaching of experience is that the conduct complained of usually is or is not blameworthy； and therefore； unless explained； is or is not a ground of liability； or it will find the jury oscillating to and fro； and will see the necessity of making up its mind for itself。 There is no reason why any other such question should not be settled； as well as that of liability for stairs with smooth strips of brass upon their edges。 The exceptions would mainly be found where the standard was rapidly changing； as； for in。 stance； in some questions of medical treatment。 /2/
＇124＇ If this be the proper conclusion in plain cases； further consequences ensue。 Facts do not often exactly repeat themselves in practice； but cases with comparatively small variations from each other do。 A judge who has long sat at nisi prius ought gradually to acquire a fund of experience which enables him to represent the common sense of the community in ordinary instances far better than an average jury。 He should be able to lead and to instruct them in detail； even where he thinks it desirable； on the whole； to take their opinion。 Furthermore； the sphere in which he is able to rule without taking their opinion at all should be continually growing。
It has often been said； that negligence is pure matter of fact； or that； after the court has declared the evidence to be such that negligence may be inferred from it； the jury are always to decide whether the inference shall be drawn。 /1/ But it is believed that the courts； when they lay down this broad proposition； are thinking of cases where the conduct to be passed upon is not proved directly； and the main or only question is what that conduct was； not what standard shall be applied to it after it is established。
Most cases which go to the jury on a ruling that there is evidence from which they may find negligence； do not go to them principally on account of a doubt as to the standard； but of a doubt as to the conduct。 Take the case where the fact in proof is an event such as the dropping of a brick from a railway bridge over a highway upon the plaintiff； the fact must be inferred that the dropping was ＇125＇ due； not to a sudden operation of weather； but to a gradual falling out of repair which it was physically possible for the defendant to have prevented； before there can be any question as to the standard of conduct。 /1/
So； in the case of a barrel falling from a warehouse window； it must be found that the defendant or his servants were in charge of it； before any question of standard can arise。 /2/ It will be seen that in each of these well…known cases the court assumed a rule which would make the defendant liable if his conduct was such as the evidence tended to prove。 When there is no question as to the conduct established by the evidence； as in the case of a collision between two trains belonging to the same company； the jury have； sometimes at least； been told in effect that； if they believed the evidence； the defendant was liable。 /3/
The principal argument that is urged in favor of the view that a more extended function belongs to the jury as matter of right； is the necessity of continually conforming our standards to experience。 No doubt the general foundation of legal liability in blameworthiness； as determined by the existing average standards of the community； should always be kept in mind； for the purpose of keeping such concrete rules as from time to time may be laid down conformable to daily life。 No doubt this conformity is the practical justification for requiring a man to know the civil law； as the fact that crimes are also generally sins is one of the practical justifications for requiring a man to know the criminal law。 But these considerations only lead to ＇126＇ the conclusion that precedents should be overruled when they become inconsistent with present conditions； and this has generally happened； except with regard to the construction of deeds and wills。 On the other hand； it is very desirable to know as nearly as we can the standard by which we shall be judged at a given moment； and； moreover； the standards for a very large part of human conduct do not vary from century to century。
The considerations urged in this Lecture are of peculiar importance in this country； or at least in States where the law is as it stands in Massachusetts。 In England； the judges at nisi prius express their opinions freely on the value and weight of the evidence； and the judges in banc； by consent of parties； constantly draw inferences of fact。 Hence nice distinctions as to the province of court and jury are not of the first necessity。 But when judges are forbidden by statute to charge the jury with respect to matters of fact； and when the court in banc will never hear a case calling for inferences of fact； it becomes of vital importance to understand that； when standards of conduct are left to the jury； it is a temporary surrender of a judicial function which may be resumed at any moment in any case when the court feels competent to do so。 Were this not so； the almost universal acceptance of the first proposition in this Lecture； that the general foundation of liability for unintentional wrongs is conduct different from that of a prudent man under the circumstances； would leave all our rights and duties throughout a great part of the law to the necessarily more or less accidental feelings of a jury。
It is perfectly consistent with the views maintained in this Lecture that the courts have been very slow to withdraw questions of negligence from the jury； without distinguishing ＇127＇ nicely whether the doubt concerned the facts or the standard to be applied。 Legal； like natural divisions； however clear in their general outline； will be found on exact scrutiny to end in a penumbra or debatable land。 This is the region of the jury； and only cases falling on this doubtful border are likely to be carried far in court。 Still； the tendency of the law must always be to narrow the field of uncertainty。 That is what analogy； as well as the decisions on this very subject； would lead us to expect。
The growth of the law is very apt to take place in this way。 Two widely different cases suggest a general distinction； which is a clear one when stated broadly。 But as new eases cluster around the opposite poles； and begin to approach each other； the distinction becomes more difficult to trace； the determinations are made one way or the other on a very slight preponderance of feeling； rather than of articulate reason； and at last a mathematical line is arrived at by the contact of contrary decisions； which is so far arbitrary that it might equally well have been drawn a little farther to the one side or to the other； but which must have been drawn somewhere in the neighborhood of ；where it falls。 /1/
In this way exact distinctions have been worked out upon questions in which the elements to be considered are few。 For instance； what is a reasonable time for presenting negotiable paper； or what is a difference in kind and what a difference only in quality； or the rule against perpetuities。
An example of the approach of decisions towards each other from the opposite poles； and of the function of the jury midway； is to be found in the Massachusetts adjudications； ＇128＇ that； if a child of two years and four months is unnecessarily sent unattended across and down a street in a large city； he cannot recover for a negligent injury； /1/ that to allow a boy of eight to be abroad alone is not necessarily negligent； /2/ and that the effect of permitting a boy of ten to be abroad after dark is for the jury； /3/ a coupled with the statement； which may be ventured on without authority； that such a permission to a young man of twenty possessed of common in