Note (return) — Chapter II

The witnesses for the prosecution and the defence, if they are well-intentioned men, often find themselves giving, to their own surprise, perfectly consistent accounts of the events at issue. The barristers' tricks of advocacy are to some extent restrained by professional custom and by the authority of the judge, and they are careful to point out to the jury each other's fallacies. Newspapers do not reach the jury box, and in any case are prevented by the law as to contempt of court from commenting on a case which is under trial. The judge sums up, carefully describing the conditions of valid inference on questions of disputed fact, and warning the jury against those forms of irrational and unconscious inference to which experience has shown them to be most liable. They then retire, all carrying in their minds the same body of simplified and dissected evidence, and all having been urged with every circumstance of solemnity to form their conclusions by the same mental process. It constantly happens therefore that twelve men, selected by lot, will come to a unanimous verdict as to a question on which in the outside world they would have been hopelessly divided, and that that verdict, which may depend upon questions of fact so difficult as to leave the practised intellect of the judge undecided, will very generally be right. An English law court is indeed during a well-governed jury trial a laboratory in which psychological rules of valid reasoning are illustrated by experiment; and when, as threatens to occur in some American States and cities, it becomes impossible to enforce those rules, the jury system itself breaks down.[73]