Every emotion, whether of the kind psychologists call sthenic, or of the asthenic sort, implies a narrowing of the field of conscious action. It favors unreasoned, associative (i.e., determined by external factors), or impulsive mental activity over a form of thinking proceeding with due consideration according to the categories of logic, especially the principle of causality (apperceptive thinking, to use the terminology of Wundt). Briefly, every emotion lessens the capacity of the intellect to see the truth, it makes partially blind. Passionless absence of emotion is a prerequisite of all scientific thinking, that is, thinking directed to the recognition of external truths.
The reason why this requirement was insisted on by lawyers at so early a period must be sought in the circumstance that the judge is exposed more than any other thinker to emotional influences. He must come to his conclusion among the struggles of contending parties. While in the case of other sciences conflicts of wills mean annoying interference, they are the natural environment for jurisprudence, in which it carries on its life functions. Moreover, the results of juridical thinking at once become matters of practical importance and touch the very nerve of life. Errors produced by emotion are felt most often and easiest in the field of legal thinking, and it is for this reason that lawyers were the first and the most emphatic in insisting on the absence of emotional bias.
The general public, with its deficient understanding of psychology, includes in this requirement merely the absence of individual emotions in the widest sense, "prejudice and bias for or against either party." That amounts, generally speaking, to the reasons which make a judge or juror incapable of acting according to most codes of procedure, such as personal interest, kinship, and the like. Modern social science, however, has shown that there exist, in addition to the influence of such individual emotions, a multitude of social feelings which exercise a determining influence on the way we think of and judge other persons. Such social feelings may be of a national or political, professional, religious character, may be produced by class, occupation, or other circumstances that produce a feeling of solidarity; or they may be based on ethical tendencies, historical traditions, inherited value judgments, and so forth. The more general and constant nature of such feelings is the reason why they do not usually take the form of an acute emotion and do not, generally speaking, enter into individual consciousness at all but remain below its threshold. Just the same, or perhaps for that very reason, they are apt to obscure the logical quality of thought and judgment in a manner quite obvious to a really unbiased observer. Anyone who desires a large number of examples showing how it is by no means enough, in order to be unbiased in regard to social currents by which one is himself carried along, if one has the intention of being unbiased, cannot do better than to turn to Spencer's "The Study of Sociology.15 There he will learn how our attitude towards the world, our whole way of thinking, is covered by a network of tendencies and cross-tendencies, how under their influence the same phenomenon may meet with the most various judgments although the critics are all imbued with the most upright desire for the truth. Modern logic (see the writings of Wundt, Erdmann, Sigwart, etc.), which has generally come close to psychology, explains these unconscious disturbances of correct thinking very well indeed.
In this connection a question arises which cannot be answered until we have progressed farther with our inquiry. Does the requirement of lack of bias mean that the judge must also disengage his reasoning from the influence of all these social feelings? Must we take the saying "pereat mundus, fiat justitia," not ironically but pathetically? Should the judge actually comply with the demand of Spinoza and never blame or praise anything human but only understand it? Must he purify his thought of everything but logical reasoning and get rid of all feeling, whether individual or social, that may disturb his logic? Is such purification possible to all? Does it ever exist?