The second part of the work turns upon the suspicion of a definite person when his own activity is interpolated as a cause of the crime. Under some conditions again, the effect of the crime on the criminal has to be examined, i.e., enrichment, deformation, emotional state, etc. But the evidence of guilt is established only when the crime is accurately and explicitly described as the inevitable result of the activity of the criminal and his activity only. This systematic work of observing and correlating every instant of the supposed activities of the accused (once the situation of the crime is defined as certainly as possible), is as instructive as it is promising of success. It is the one activity which brings us into touch with bare perception and its reproduction. “All inference with regard to facts appears to depend upon the relation of cause to effect; by virtue of this relation alone may we rely upon the evidence of our memories and our senses.”[131] Hume illustrates this remark with the following example: If a clock or some other machine is found on a desert island, the conclusion is drawn that men are or were on the island. The application is easy enough. The presence of a clock, the presence of a three-cornered wound is perceived by the senses--that men were there, that the wound was made with a specific kind of instrument, is a causal inference. Simple as this proposition of Hume’s is, it is of utmost importance in the law because of the permanent and continually renewed problems: What is the effect in _this_ case? What is the cause? Do they belong together? Remembering that these questions make our greatest tasks and putting them, even beyond the limit of disgust, will save us from grave errors.
There is another important condition to which Hume calls attention and which is interpreted by his clever disciple Meinong. It is a fact that without the help of previous experience no causal nexus can be referred to an observation, nor can the presence of such be discovered in individual instances. It may be postulated only. A cause is essentially a complex in which every element is of identical value. And this circumstance is more complicated than it appears to be, inasmuch as it requires reflection to distinguish whether only one or more observations have been made. Strict self-control alone and accurate enumeration and supervision will lead to a correct decision as to whether one or ten observations have been made, or whether the notion of additional observations is not altogether illusory.