。 So it is held that； in cases where he is the plaintiff； an infant of very tender years is only bound to take the precautions of which an infant is capable； the same principle may be cautiously applied where he is defendant。 /1/ Insanity is a more difficult matter to deal with； and no general rule can be laid down about it。 There is no doubt that in many cases a man may be insane； and yet perfectly capable of taking the precautions； and of being influenced by the motives； which the circumstances demand。 But if insanity of a pronounced type exists； manifestly incapacitating the sufferer from complying with the rule which he has broken； good sense would require it to be admitted as an excuse。
Taking the qualification last established in connection with the general proposition previously laid down； it will ＇110＇ now be assumed that； on the one hand； the law presumes or requires a man to possess ordinary capacity to avoid harming his neighbors； unless a clear and manifest incapacity be shown； but that； on the other； it does not in general hold him liable for unintentional injury； unless； possessing such capacity； he might and ought to have foreseen the danger； or； in other words； unless a man of ordinary intelligence and forethought would have been to blame for acting as he did。 The next question is； whether this vague test is all that the law has to say upon the matter； and the same question in another form； by whom this test is to be applied。
Notwithstanding the fact that the grounds of legal liability are moral to the extent above explained； it must be borne in mind that law only works within the sphere of the senses。 If the external phenomena； the manifest acts and omissions； are such as it requires； it is wholly indifferent to the internal phenomena of conscience。 A man may have as bad a heart as he chooses； if his conduct is within the rules。 In other words； the standards of the law are external standards； and； however much it may take moral considerations into account； it does so only for the purpose of drawing a line between such bodily motions and rests as it permits； and such as it does not。 What the law really forbids； and the only thing it forbids； is the act on the wrong side of the line； be that act blameworthy or otherwise。
Again； any legal standard must； in theory； be one which would apply to all men； not specially excepted； under the same circumstances。 It is not intended that the public force should fall upon an individual accidentally； or at the whim of any body of men。 The standard； that is； ＇111＇ must be fixed。 In practice； no doubt； one man may have to pay and another may escape； according to the different feelings of different juries。 But this merely shows that the law does not perfectly accomplish its ends。 The theory or intention of the law is not that the feeling of approbation or blame which a particular twelve may entertain should be the criterion。 They are supposed to leave their idiosyncrasies on one side； and to represent the feeling of the community。 The ideal average prudent man； whose equivalent the jury is taken to be in many cases； and whose culpability or innocence is the supposed test； is a constant； and his conduct under given circumstances is theoretically always the same。
Finally； any legal standard must； in theory； be capable of being known。 When a man has to pay damages； he is supposed to have broken the law； and he is further supposed to have known what the law was。
If； now； the ordinary liabilities in tort arise from failure to comply with fixed and uniform standards of external conduct； which every man is presumed and required to know； it is obvious that it ought to be possible； sooner or later； to formulate these standards at least to some extent； and that to do so must at last be the business of the court。 It is equally clear that the featureless generality； that the defendant was bound to use such care as a prudent man would do under the circumstances； ought to be continually giving place to the specific one； that he was bound to use this or that precaution under these or those circumstances。 The standard which the defendant was bound to come up to was a standard of specific acts or omissions； with reference to the specific circumstances in which he found himself。 If in the whole department of ＇112＇ unintentional wrongs the courts arrived at no further utterance than the question of negligence； and left every case； without rudder or compass； to the jury； they would simply confess their inability to state a very large part of the law which they required the defendant to know； and would assert； by implication； that nothing could be learned by experience。 But neither courts nor legislatures have ever stopped at that point。
》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 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。
The same course of specification which has been illustrated from the statute… book ought also to be taking place in the growth of judicial decisions。 That this should happen is in accordance with the past history of the law。 It has been suggested already that in the days of the assize and jurata the court decided whether the facts constituted a ground of liability in all ordinary cases。 A question of negligence might； no doubt； have gone to the jury。 Common sense and common knowledge are as often sufficient to determine whether proper care has been taken of an animal； as they are to say whether A or B owns it。 The cases which first arose were not of a kind to suggest analysis； and negligence was used as a proximately simple element for a long time before the need or possibility of analysis was felt。 Still； when an issue of this sort is found； the dispute is rather what the acts or omissions of the defendant were than on the standard of conduct。 /1/ The ＇115＇ distinction between the functions of court and jury does not come in question until the parties differ as to the standard of conduct。 Negligence； like ownership； is a complex conception。 Just as the latter imports the existence of certain facts； and also the consequence （protection against all the world） which the law attaches to those facts； the former imports the existence of certain facts （conduct） and also the consequence （liability） which the law attaches to those facts。 In most cases the question is upon the facts； and it is only occasionally that one arises on the consequence。
It will have been noticed how the judges pass on the defendant's acts （on grounds of fault and public policy） in the case of the thorns； and that in Weaver v。 Ward /1/it is said that the facts constituting an excuse； and showing that the defendant was free from negligence； should have been spread upon the record； in order th