criminal psychology-第43部分

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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