criminal psychology-第43节
按键盘上方向键 ← 或 → 可快速上下翻页，按键盘上的 Enter 键可回到本书目录页，按键盘上方向键 ↑ 可回到本页顶部！
————未阅读完？加入书签已便下次继续阅读！
ence； or at least to set aside some one thing。 Sup… pose that the issue deals with a discovered； well…retained footprint of a man。 We then suspect somebody and compare the sole of his shoe with the impression。 They fit in length and width； in the number of nails and in all the other possible indices； and we therefore assert： It is the footprint of the suspect； for ‘‘whose footprint？'' is the problem we are troubling ourselves to solve。 In truth we have only shown that the particular relations； in the matter of length； breadth； number of nails； etc。； agree； and hence we regard the positive part of the evidence as sufficient and neglect the whole troublesome negative part； which might establish the fact that at the time and in the region in question； nobody was or could be whose foot could accurately fit that particular footprint。 Therefore we have not proved but have only calculated the probability that at the time there might possibly not have been another person with a shoe of similar length； breadth and number of nails。 The probability becomes naturally less as fewer details come to hand。 The difficulty lies in finding where such probability； which stands for at least an assumption； must no longer be considered。 Suppose； now； that neither shoe…nails nor patches； nor other clear clews can be proved and only length and width agree。 If the agreement of the clews were really a substantiation of the proof by evidence； it would have to suffice as positive evidence； but as has been explained； the thing proved is not the point at issue； but another point。
The negative portion of the evidence will naturally be developed with less accuracy。 The proof is limited to the assertion that such shoes as were indicated in the evidence were very rarely or never worn in that region； also that no native could have been present that the form of the nails allowed inference of somebody from foreign regions； one of which might be the home of the suspect； etc。 Such an examination shows that what we call evidence is only probability or possibility。
Another form which seems to contradict the assertion that negative propositions are infinite is positive evidence in the shape of negation。 If we give an expert a stain to examine and ask him whether it is a blood stain； and he tells us： ‘‘It is not a blood stain；'' then this single scientifically established assertion proves that we do not have to deal with blood； and hence ‘‘negative'' proof seems brought in a single instance。 But as a matter of fact we deal here with an actually positive proof； for the expert has given us the deduced proposition； not the essential assertion。 He has found the stain to be a rust stain or a tobacco stain； and hence he may assert and deduce that it is not blood。 Even were he a skeptic； he would say； ‘‘We have not yet seen the blood of a mammal in which the characteristic signs for recognition were not present； and we have never yet recognized a body without the blood pertaining to it； and hence we may say； we are not dealing with blood because all of us found the characteristics of the stain to be what we have been until now accustomed to call the characteristics of rust stain。''
We have still to touch upon the difference between logical connection and experience。 If I say； ‘‘This mineral tastes salty； therefore it is soluble in water；'' the inference depends upon logical relationships； for my intent is： ‘‘If I perceive a salty taste； it has to be brought to the nerves of taste； which can be done only by the combination of the mineral with the saliva； hence by its solution in the saliva。 But if it is soluble in saliva it must also be soluble in water。'' If I say on the other hand； ‘‘This mineral tastes salty； has a hardness of 2； a specific gravity of 2。2； and consequently it crystallizes hexagonally；''this statement depends on experience； for what I really say is： ‘‘I know first of all； that a mineral which has the qualities mentioned must be rock salt； for at the least； we know of no mineral which has these qualities and is not rock salt； and which in the second place crystallizes hexagonally as rock salt does；a way which； at least； we find rock salt never to have missed。'' If we examine the matter still more closely we become convinced that in the first case only the formal and logical side； in the second the experiential aspect predominates。 The premises of both cases are purely matters of experience and the formal question of inference is a matter of logic。 Only；at one time the first question； at another the second comes more obviously into the foreground。 Although this matter appears self…evident it is not indifferent。 It is well known that whenever we are powerfully influenced by one thing； things of little intensity are either not experienced at all or only to a very small degree； and are therefore neglected。 This is a fact which may indeed be shown mathematically； for infinity plus one equals infinity。 When； therefore； we undergo great pain or great joy； any accompanying insignificant pain or any pleasure will be barely felt； just as the horses who drag a very heavy wagon will not notice whether the driver walking beside them adds his coat to the load （cf。 Weber's law）。 Hence； when we criminalists study a difficult case with regard to the question of proof； there are two things to do in order to test the premises for correctness accord… ing to the standards of our other experiences； and to draw logically correct inferences from these premises。 If it happens that there are especial difficulties in one direction while by some chance those in the other are easily removed； it becomes surprising how often the latter are entirely ignored。 And hence； the adjustment of inferences is naturally false even when the great difficulties of the first type are removed correctly。 Therefore； if the establishment of a fact costs a good deal of pains and means the expenditure of much time； the business of logical connection appears so comparatively easy that it is made swiftly andwrongly。
Mistakes become； at least according to my experience； still more frequent when the difficulty is logical and not empirical。 As a matter of honesty； let me say that we criminalists are not trained logicians； however necessary it is that we shall be such； and most of us are satisfied with the barren remainder of what we learned long ago in the Gymnasium and have since forgotten。 The difficulties which occur in the more important logical tasks are intelligible when compared with the lesser difficulties； and when one of these larger problems is by good fortune rightly solved； the effort and the work required by the solution make it easy to forget asking whether the premises are correct； they are assumed as self…evident。 Hence； in the review of the basis for judgment； it is often discovered that the logical task has been performed with care； with the expenditure of much time； etc。； only to be based upon some apparently unessential presupposition which contradicts all experience and is hence materially incorrect。 Consequence；the inference is wrong since the premise was wrong； and the whole work has gone for nothing。 Such occurrences convince one that no judge would have been guilty of them if the few difficulties concerning the fact in question were not； because treated in the light of the effort required by the logical work； quite neglected。 Nor does this occur unconsciously； or as a consequence of a sort of lapse of memory concerning the meaning or the importance of an empirical problem； it also happens at least half consciously by way of a characteristic psychic process which everybody may identify in his own experience： i。 e。； the idea occurs； in some degree subconsciously； that the overgreatness of the work done in one direction ought to be corrected by the inadequacy of the work done in the other direction。 And this happens in lawyer's work often； and being frequently justifiable； becomes habitual。 If I； for example； have examined ten unanimous witnesses concerning the same event and have completely demonstrated the status of the case； I ought； in examining the last two witnesses； who are perhaps no longer needed but have been summoned and appear； certainly to proceed in a rapid manner。 This justifiable neglect is then half unconsciously transferred to other procedures where there is possible no equalization of the hypertrophy of work in one direction with the dwarfing of it in another； and where the mistake causes the result to be wrong。 However I may have been bothered by the multiplication of ten groups of factors and whatever accuracy I may have applied to a task can not permit me to relax my attention in the addition of the individual results。 If I do I am likely to commit an error and the error renders all the previous labor worthless。
Indeed； it may be asserted that all logic is futile where the premises or a single premise may be wrong。 I expect； in truth； that the procedures here described will be doubted to be even possible； but doubters are recommended to examine a few cases for the presence of this sort of thing。
Section 27。 （e） Analogy。
Analogy is the least negligible of all methods of induction because it rests at bottom on the postulate that on
