It  is  clear  that  the  doctrine  may  easily  degenerate  into  rhetoric .sx   We  find  , for  example  , so  weighty  a  writer  as  Best  , in  his  classic  treatise  on  Evidence  , basing  the  doctrine  on  a  still  broader  one  , which  he  claims  that  `the  legislators  and  jurists  of  almost  every  age  and  country  have  recognized'    namely  , that  `the  protection  of  innocence'  is  `the  primary  care  of  the  law' .sx   If  the  legislators  and  jurists  of  almost  every  age  and  country  have  believed  this  , they  have  pinned  their  faith  to  a  transparent  fallacy .sx   The  law  may  exist  to  protect  a  great  many  things  , but  it  does  not  exist  to  protect  innocence .sx   Guilt  means  that  the  law  has  been  broken  , innocence  means  that  it  has  not  been  broken  ; and  there  is  no  necessity  for  the  law  to  `protect'  a  person  who  has  not  infringed  it :sx   for  against  what  is  he  protected   ?sx   Who  or  what  is  attacking  him  for  not  having  broken  the  law ?sx   Why  need  he  be  defended  against  imaginary  aggression   ?sx   When  he  is  acquitted  of  a  criminal  charge  , it  is  not  a  case  of  `protecting'  , but  of  merely  declaring  , innocence .sx   The  compulsory  sanctions  of  law  exist  in  order  to  protect  rights  or  impose  duties  , or  both  things  together  ; and  it  is  really  necessary  to  remind  ourselves  sometimes  that  penal  law  exists  in  order  to  prevent  disobedience  , not  to  vindicate  obedience .sx   Law  punishes  lawlessness  ; seldom  or  never  does  it  reward  lawfulness .sx   
Again  , 'it  is  better  that  ten  guilty  persons  should  be  acquitted  than  that  one  innocent  person  should  be  convicted' .sx   As  Stephen  dryly  observes  , it  all  depends  on  what  the  guilty  persons  have  been  doing .sx   It  also  depends  on  the  general  social  conditions  in  which  they  have  been  doing  it .sx   I  have  already  called  attention  to  the  vague  fluctuations  in  the  proverbial  ratio  between  the  guilty  and  the  innocent  ; and  I  have  done  so  in  no  spirit  of  levity  , for  the  ratio  which  it  assumes  is  not  without  significance .sx   I  dare  say  some  sentimentalists  would  assent  to  the  proposition  that  it  is  better  that  a  thousand  , or  even  a  million  , guilty  persons  should  escape  than  that  one  innocent  person  should  suffer  ; but  no  sensible  and  practical  person  would  accept  such  a  view .sx   For  it  is  obvious  that  if  our  ratio  is  extended  indefinitely  , there  comes  a  point  when  the  whole  system  of  justice  has  broken  down  and  society  is  in  a  state  of  chaos .sx   In  short  , it  is  only  when  there  is  a  reasonable  and  uniform  probability  of  guilty  persons  being  detected  and  convicted  that  we  can  allow  humane  doubt  to  prevail  over  security .sx   But  we  must  never  forget  that  ideally  the  acquittal  of  ten  guilty  persons  is  exactly  ten  times  as  great  a  failure  of  justice  as  the  conviction  of  one  innocent  person .sx   
Again  , `in  a  civil  case  a  preponderance  of  probabilities  is  sufficient  , but  in  a  criminal  case  the  prisoner's  guilt  must  be  proved  beyond  all  reasonable  doubt' .sx   This  statement  is  constantly  repeated  in  the  text-books  , but  very  little  authority  is  cited  for  it  , and  it  is  difficult  to  know  what  real  meaning  is  to  be  attached  to  it .sx   Certainly  it  cannot  mean  that  there  is  any  substantive  difference  ( except  perhaps  in  certain  offences  where  corroboration  is  required  ) between  the  methods  of  proof  in  civil  and  criminal  cases  , for  it  is  laid  down  again  and  again  that  this  is  not  the  law .sx   Is  there  any  true  difference  between  a  preponderance  of  probabilities  and  a  reasonable  certainty  ( the  converse  of  reasonable  doubt  )  ?sx   `Probability'  may  mean  different  things .sx   It  is  often  loosely  used  to  indicate  mere  conjecture  or  plausibility .sx   Neither  in  civil  nor  in  criminal  cases  is  a  jury  entitled  to  consider  an  averment  established  by  conjecture  or  plausibility .sx   But  `probability'  may  also  mean  the  utmost  degree  of  certainty  or  conviction  which  , upon  the  evidence  of  circumstances  , things  and  statements  , can  be  attained  by  our  limited  powers  of  reasoning  and  observation .sx   
That  degree  of  certainty  or  conviction  exists  , or  ought  to  exist  , in  the  decision  of  any  legal  issue .sx   It  is  difficult  to  see  how  men  and  women  , called  upon  to  weigh  evidence  either  in  civil  or  criminal  matters  , can  bring  to  bear  anything  more  than  Pollock  C.B.  requires  of  them    i.e.  `that  degree  of  certainty  that  you  would  act  upon  in  your  own  grave  and  important  concerns'  ;  for  indeed  they  have  no  other  means  of  reasoning .sx   The  principle  of  'reasonable  doubt'  therefore  seems  to  be  little  more  than  a  counsel  of  prudence  ; and  there  is  considerable  judicial  authority  for  this  view .sx   The  warning  is  not  so  frequently  uttered  in  civil  cases  , because  the  occasion  is  not  so  solemn  ; but  does  it  follow  that  the  same  degree  of  care  and  certainty  is  not  as  necessary  , or  at  least  as  desirable  , in  the  one  case  as  in  the  other   ?sx   I  apprehend  that  a  judge  who  directed  a  jury  in  an  action  for  damages  , `You  need  not  be  as  careful  in  arriving  at  your  conclusions  as  if  you  were  trying  a  criminal  case'  , would  considerably  startle  the  legal  world  and  the  public  ; and  though  there  is  a  good  reason  for  reminding  juries  of  the  necessity  for  caution  in  criminal  cases  , I  know  of  no  authority  for  the  proposition  that  their  duty  is  any  less  when  property  , and  not  life  or  liberty  , is  at  stake .sx   
Finally  , it  is  noteworthy  that  the  presumption  of  innocence  , firmly  established  though  it  is  , and  salutary  though  it  is  within  its  proper  limits  , is  not  without  important  exceptions .sx   Statutory  offences  involving  little  or  no  mens  rea  are  common  nowadays  , and  it  would  seem  that  in  many  of  these  cases  the  mere  fact  of  non-compliance  with  a  positive  duty  , which  has  been  imposed  by  statute  , raises  a  presumption  of  guilt .sx   Thus  in  Huggins  v.  Ward  ( 1873  ) , L.R.  8  Q.B.  521  , the  duty  in  question  was  that  of  giving  notice  `with  all  practicable  speed'  to  the  police  of  a  contagious  disease  among  animals .sx   It  was  held  that  the  mere  fact  of  possessing  diseased  animals  was  prima  facie  evidence  of  a  breach  of  the  statute  , and  the  onus  lay  on  the  defendant  of  proving  that  he  had  given  notice .sx   Similarly  in  Over  v.  Harwood  , 1900  I  Q.B.  803  , it  was  held  that  evidence  that  a  certificate  of  vaccination  had  not  been  received  by  the  proper  officer  was  prima  facie  evidence  of  breach  of  the  statute  which  required  the  certificate    no  doubt  a  rule  essential  to  practical  administrative  convenience  , but  somewhat  startling  when  we  remember  that  there  are  a  dozen  ways  in  which  a  certificate  which  has  been  duly  sent  may  be  lost  or  mislaid .sx   Cases  like  these  can  only  mean  that  when  a  positive  statutory  provision  has  not  been  complied  with  , the  person  who  is  alleged  to  have  broken  it  is  deemed  to  be  guilty  until  he  has  explained  himself  satisfactorily :sx   and  it  seems  a  little  paradoxical  when  the  Court  adds  , in  Over  v.  Harwood  , that  the  burden  of  proving  non-compliance  rests  on  the  prosecution .sx   
Further  , the  law  has  been  compelled  to  modify  in  some  important  respects  the  principle  that  a  man  is  entitled  to  come  before  the  jury  with  a  clean  sheet  , whatever  his  previous  conduct  may  have  been .sx   For  example  , the  receiver  of  stolen  goods  is  a  criminal  who  is  all  the  more  dangerous  because  he  is  cowardly  , and  experience  showed  that  under  the  Common  Law  he  frequently  escaped  because  of  the  difficulty  of  proving  affirmatively  his  knowledge  of  the  guilty  origin  of  the  booty .sx   In  1871  , therefore  , it  was  found  necessary  to  enact  that  on  such  a  charge  evidence  may  be  given  that  stolen  property  has  been  found  in  the  possession  of  the  accused  within  the  previous  twelve  months .sx   A  recent  suspicious  circumstance  of  this  kind  , it  would  be  generally  agreed  , is  not  unfairly  relevant  to  a  charge  of  receiving  ; but  the  statute  goes  on  to  provide  that  evidence  may  also  be  given  of  a  conviction  for  `any  offence  involving  fraud  or  dishonesty'  within  the  previous  five  years .sx   Though  it  is  probably  a  highly  expedient  , this  certainly  is  not  a  lenient  provision  , for  there  may  easily  be   .sx
circumstances  in  which  it  is  a  far  cry  from  a  fraud  committed  five  years  ago  , to  a  receiving  of  stolen  goods  to-day .sx   An  enactment  of  this  kind  shows  , if  I  may  return  to  a  former  point  , that  society  cannot  `afford  to  be  generous'  to  receivers  , for  society  very  well  knows  that  this  elusive  type  of  criminal  is  an  instigator  and  an  organizer  , on  a  large  scale  , of  offences  against  property .sx   
But  perhaps  the  most  conspicuous  modification  of  the  principle  that  the  accused  is  not  to  be  prejudiced  by  his  previous  misdeeds  or  evil  reputation  is  the  development  of  the  doctrine  relating  to  what  is  called  `system'  or  `systematic  course  of  conduct' .sx   I  do  not  think  it  is  generally  realized  how  much  this  doctrine  has  grown  and  how  seriously  it  has  eaten  into  the  principle  that  'conduct  on  other  occasions'  is  inadmissible  in  evidence  against  a  prisoner .sx   So  far  as  I  can  discover  , the  doctrine  first  made  its  appearance  at  the  beginning  of  the  nineteenth  century  , and  it  arose  for  a  very  good  reason .sx   At  that  time  , if  one  may  judge  by  the  number  of  reported  decisions  upon  the  matter  , there  seems  to  have  been  something  like  an  epidemic  of  forgery  and  uttering .sx   Now  , there  is  an  easy  defence  to  a  charge  of  uttering  false  coin  or  bank-notes   :sx   the  accused  will  almost  certainly  say  that  the  money  came  into  his  possession  innocently  and  that  he  had  no  notion  that  it  was  false  ; and  it  is  extremely  difficult  to  prove  his  guilty  knowledge .sx   A  jury  , however  , will  not  be  likely  to  regard  it  as  a  mere  coincidence  if  it  is  shown  that  the  accused  has  done  the  same  thing  on  previous  occasions .sx   In  1801  , in  R.  v.  Tattershall  , a  case  referred  to  in  2  Leach  984  , but  otherwise  unreported  , Chambre  J.  laid  it  down  at  Nisi  Prius  that  evidence  of  previous  uttering  might  be  admitted  against  a  person  charged  with  that  offence .sx   Three  years  later  , in  R.  v.  Whiley  ( 1804  ) , 2  Leach  983  , Chambre  J.  was  confirmed  in  that  view  by  the  full  Court  of  King's  Bench  , presided  over  by  Lord  Ellenborough .sx   This  decision  was  immediately  followed  in  several  cases  , though  as  late  as  1829  Bayley  J.  expressed  doubts  about  it .sx   It  was  soon  extended  to  other  offences  ; thus  in  R.  v.  Hunt  ( 1820  ) , 3  B.  &  Ald .sx   566  , it  was  held  that  on  a  charge  of  sedition  evidence  might  be  given  of  previous  seditious  acts  , utterances  and  preparations  ; and  in  R.  v.  Yoke  ( 1823  ) , Russ .sx   &  Ry .sx   531  , where  on  a  charge  of  shooting  evidence  was  admitted  of  a  previous  shooting  at  the  same  person  , we  hear  the  now  familiar  doctrine  that  evidence  of  previous  similar  conduct  may  be  given  in  order  to  rebut  the  defence  of  accident .sx   A  turning-point  was  reached  in  1849  with  R.  v.  Geering  , 18  L.J.  M.C.  215  , where  it  was  held  , on  a  charge  of  husband-poisoning  , that  evidence  might  be  given  of  the  deaths  from  poisoning  of  other  members  of  the  family  whose  food  the  prisoner  had  prepared .sx   Since  that  date  , the  doctrine  has  undoubtedly  extended  its  scope  with  rapidity  and  elasticity .sx   For  a  long  time  , and  even  after  the  important  decision  of  the  Judicial  Committee  in  Makin  v.  Att .sx -Gen.  for  New  South  Wales  , 1894  A.C.  57  , it  was  sought  to  restrain  the  doctrine  to  the  purpose  either  of  rebutting  a  defence  of  accident  or  mistake  or  else  of  proving  a  particular  intent  which  constituted  an  integral  part  of  the  offence  ; and  as  late  as  1915  , this  limit  is  reasserted  by  the  King's  Bench .sx   But  there  are  many  signs  that  of  recent  years  this  limitation  has  been  gradually  relaxed .sx   Thus  there  has  been  an  increasing  number  of  cases  in  which  evidence  has  been  admitted  of  similar  acts  done  not  only  before  , but  after  , the  offence  charged  ; and  this  kind  of  evidence  has  been  admitted  in  order  to  rebut  a  defence  of  alibi  and  mistaken  identity    a  very  different  thing  from  a  defence  of  `accident  or  mistake' .sx   On  charges  of  sexual  offences  , there  has  been  a  tendency  to  admit  evidence  of  similar  previous  acts  committed  some  considerable  time  before  , which  could  hardly  be  regarded  as  constituting  a  'system'  ; and  in  the  two  most  recent  cases  , a  very  important  extension  has  been  made    viz .sx   that  evidence  either  of  previous  or  of  subsequent  conduct  may  be  given  in  order  to  negative  a  defence  of  'innocent  intent' .sx