ABSTRACT
THE connexion between a mass of evidence and that which it evinces may be approached from two different points of view. The first is exemplified in the attitude of legal counsel, for the defence, or for the prosecution; the second, in the attitude of a detective attempting to discover the man who did the deed. For brevity, we may refer to the mass of evidence as the data, and to that which it evinces as the probandum. The counsel accepts the probandum as already determined; his problem is to select from miscellaneous, and possibly conflicting data, just those facts which point to the already accepted probandum. The detective seeks a probandum which is, at the outset, completely undetermined; his problem is to determine the probandum by examining the data, selecting what is relevant, and recognizing its significance. His selection is guided by an hypothesis, more or less capable of explicit formulation. His thinking involves the three steps mentioned in Chapter I; if the conditions constituting the problem are at all complicated, he may need to try out several hypotheses before he is satisfied that he has hit upon the correct solution. The detective’s task is more difficult than that of the counsel. The data may point in many different directions; at first sight it may even be the case that no definite probandum appears to be indicated by the available data. Once the case is completed, the detective, no less than the counsel, may present his conclusions in deductive form. Nevertheless, his reasoning remains essentially inductive. For example, the detective may argue: ‘A’s boots fit these footprints in the flower-bed; therefore, A made these footprints.’ The cogency of this argument would depend upon certain assumptions, e.g. that one person’s boots are discernibly different in shape from any one else’s, and that footprints 68in flower-beds can reveal the differences between the boots that caused them and all other boots. When the assumptions, are made explicit the generalizations involved therein are obviously far from being certain. A detective’s argument will be much stronger when it is based on the generalization that no two people have the same fingerprints. The warrant for this assumption is to be found in the observed fact that every person tested for finger-prints is found to have peculiar markings. It should not be necessary to multiply illustrations of the contention that the significance of the observed facts—constituting the original data—is wholly due to our knowledge of the regular ways in which one happening is connected with other happenings. The cogency of the counsel’s argument depends likewise upon the previous acceptance of premisses obtained by inductive generalization.
