The significant fact in regard to the procedures of justice is that they are of men, by men, and for men. Any attempt to eliminate unduly the human element, or to esteem a system apart from its adaptation to the psychology of human traits as they serve the ends of justice, is likely to result in a machine-made justice and a mechanical administration. As a means of furthering the plasticity of the law, of infusing it with a large human vitality--a movement of large scope in which religion and ethics, economics and sociology are worthily cooperating--the psychology of the party of the first part and the party of the second part may well be considered. The psychology of the judge enters into the consideration as influentially as the psychology of the offender. The many-sidedness of the problems thus unified in a common application is worthy of emphasis. There is the problem of evidence: the ability of a witness to observe and recount an incident, and the distortions to which such report is liable through errors of sense, confusion of inference with observation, weakness of judgment, prepossession, emotional interest, excitement, or an abnormal mental condition. It is the author’s view that the judge should understand these relations not merely in their narrower practical bearings, but in their larger and more theoretical aspects which the study of psychology as a comprehensive science sets forth. There is the allied problem of testimony and belief, which concerns the peculiarly judicial qualities. To ease the step from ideas to their expression, to estimate motive and intention, to know and appraise at their proper value the logical weaknesses and personal foibles of all kinds and conditions of offenders and witnesses,--to do this in accord with high standards, requires that men as well as evidence shall be judged. Allied to this problem which appeals to a large range of psychological doctrine, there is yet another which appeals to a yet larger and more intricate range,--that of human character and condition. Crimes are such complex issues as to demand the systematic diagnosis of the criminal. Heredity and environment, associations and standards, initiative and suggestibility, may all be condoning as well as aggravating factors of what becomes a “case.” The peculiar temptations of distinctive periods of life, the perplexing intrusion of subtle abnormalities, particularly when of a sexual type, have brought it about that the psychologist has extended his laboratory procedures to include the study of such deviation; and thus a common set of findings have an equally pertinent though a different interest for the theoretical student of relations and the practitioner. There are, as well, certain special psychological conditions that may color and quite transform the interpretation of a situation or a bit of testimony. To distinguish between hysterical deception and lying, between a