CHAPTER VIIEVIDENCE
After you have marshaled the facts you wish to prove, you must consider the classes of evidence by which you wish to prove them.
In the first place there is the direct statement of the facts by witnesses, or the opinions of those witnesses who are qualified to speak as experts. Then there is circumstantial evidence, which consists of inferences fairly drawn from facts; in other words reasoning about facts. Thus if you wish to prove that cutting the forest off the northern part of the lower peninsula of Michigan has lessened the rainfall in that State, you could present three classes of testimony. You could bring forward an old resident who had known Michigan when it was wooded and when it was stripped of its timber; if from his own personal observation he could testify that as the timber was cut off the rainfall had diminished, that would be direct evidence of that fact. If you presented the statements of a scientist who would testify that when lands were stripped of their trees, there was less rainfall, his opinions would be entitled to consideration as proof of the facts just inthe proportion that his observation and experience had been extended and at the same time exact.
Circumstantial Evidence.—If the cutting of the forests in Minnesota near the head waters of the Mississippi was under discussion, you might present the testimony of a man who lived on the banks of that river in Iowa, who had never seen Minnesota, but who could testify that the volume of water in the river had decreased from year to year in certain proportion. His testimony would be valuable as tending to establish your position, if you could also show that the cutting of the timber in Minnesota had proceeded in the same ratio as the decrease in the river’s volume. It would then be a fair inference that the two facts were so connected that one tended to prove the other.
The line, however, between direct and circumstantial evidence is very faint—one imperceptibly glides into the other. Indeed some experts insist that there is no such thing as direct evidence. They urge that all proof consists of deductions which may be so closely related to the fact to be established that a mere statement conclusively shows the causal relation. On the other hand this relation can frequently be shown only by the most delicate fitting together of all the links of circumstance. For example, suppose the testimony of A is that he saw B point a gun at C, that the gun was fired, that immediately C fell dead. His testimony would be,therefore, that B shot C and you, if you were on the jury, would perhaps feel justified in finding B guilty of murder—there would seem to be no doubt about it. But after all, his testimony is not direct evidence—even as simple and apparently as conclusive a statement as his might be explained away. Suppose, for example, an autopsy showed that C had heart disease and fell dead from that cause, and that the bullet penetrated C’s arm only. What to the observer would seem like irrefutable proof would be dissipated in a moment; it would be shown to be an unwarrantable deduction from certain circumstances.
Remember, however, that the value of evidence is in this ratio: that direct evidence of a witness who knows of his own knowledge and observation in the particular case is more to be trusted than expert evidence based on general observation, and that both are worth more than that evidence which is the result of deduction and inference.
Qualifications of Witnesses.—In weighing the value of the testimony offered to prove your facts—testimony is those statements of the witness which make up his evidence—you must ask him certain questions. If he were a witness in a law suit, the lawyers would bring out the points you must determine by four questions. Following their example, you will first ask “Is he honest or prejudiced?” In the conservation question considered,you would ask whether he was the agent of a lumber company whose statements would naturally be influenced by his selfish interest, or a homesteader who, since his only use for land was for farming purposes, would likely be as prejudiced the other way, or was he a banker or merchant who served both classes equally, whose interest lay equally with each party to the controversy?
You will next ask if his testimony is consistent with known facts. If he testified that the absence of trees had nothing to do with rainfall and had cited as proof of that alleged fact that there was a heavy rainfall in Sahara where there were no trees, you could at once dismiss him as an impossible witness because his statements as to Sahara were inconsistent with the known facts.
You should then inquire under what circumstances were the statements made: were they forced from him, were his relations such that he was a voluntary and willing witness endeavoring to assist investigation and find out the facts? If so, his testimony is probably valuable and worthy of credence.
Then in the last place, if the statements are made as those of an expert, the value of his testimony is in the exact ratio of his experience in the particular field discussed. Here is the opportunity for a very common error in argument. Frank in debating might have urged the opinion of Professor A or Doctor B, and Jack in his reply urged confidentlythe opinions of Judge C or General D as disposing of the evidence of Frank’s witnesses. But they would simply offset one opinion with another unless Jack could show that the judge and the general knew more about the subject matter than the professor and the doctor. Character or standing or position would avail nothing. In discussing conservation, for example, the opinion of the most eminent professor in a theological school or the greatest expert inrunning electric carswould not be received in questions of soil moisture or timber culture. It is not the standing of the man generally; it is his knowledge of the subject discussed, which makes his opinions acceptable as evidence. The evidence of a farmer or hunter or trapper, although unable to read or write, might outweigh that of the so-called expert.
Generalizations.—Next, in weighing circumstantial evidence, you will observe that there are three common forms in which it appears. There is first the generalization—very frequently the shape an expert’s opinion takes. If he says that timber tracts are worth so many dollars an acre as timber and so many dollars an acre as farms, his opinion is valuable or not depending upon what the basis of his judgment is. If it develops that he has observed many hundreds of such tracts of land, and that these different tracts lay in many different places, you safely conclude that his testimony, although ageneralization, is sound because it is based upon wide observation. If he has inspected but very few such tracts, you conclude that his generalization is unsound, and worthless in helping you prove the facts.
Do not hesitate to apply the probe to the qualifications of your opponent’s expert, but be equally sure you establish the right of your own witness to speak as such. For example, I remember a case where the question involved was whether dehorning cattle was cruel within the meaning of a statute forbidding cruelty to animals. One side brought forward as expert professional witnesses certain surgeons eminent in their profession. They testified that the horn of the cow contained just under the hard bony shell a thin membranous structure, the extension of the periosteum, which was very sensitive to pain. They testified that they had known of cases where the shell of the horn had been removed by accident and this membrane exposed, whereupon the animals had given every manifestation of suffering excruciating pain. They argued from the sensitiveness of the periosteum, through these few instances of accident, to the deduction that dehorning cows, that is, sawing the horn off at right angles to this membrane, must also be extremely painful and hence cruel.
Opposed to these expert opinions of these surgeons based upon these few cases, were the opinionsof farmers who did not pretend to have the scientific knowledge of the surgeons but whohad dehorned many cows. They testified that they had seen but slight evidences of pain, that the animals had shown annoyance rather than distress, and had generally at once gone to eating. The farmers had no titles or university degrees; the experts had both, and supposedly in the very field of the debate—for that was what it was, although in a court of law. The superior qualifications of the plain unlettered farmers made their evidence of much greater value as expert testimony than the deductions of the expert gentlemen from the city.
Suppose you are discussing the adoption of a law prohibiting child labor. You can quote with confidence the opinion of a social worker whose daily duties keep her among operatives in mills. By her daily observation she is in a position to know the evil effects of labor on immature bodies and minds. So is the doctor or the teacher who sees these children daily. On the other hand, the farmer, who, although honest in his deduction from the results of his own labor, is not qualified because he himself worked as a boy on a farm to speak understandingly of the effects of child labor in mills or factories. He must confine his testimony to the effect of child labor on the farm. Nor is the woman who knows nothing of labor on farm or in factory qualified to speak at all, sentimentally aroused asshe may be, unless she can show observation of conditions herself or the intelligent study of the well founded opinions of others.
Cause and Effect.—Then again there is in circumstantial evidence the inference you draw from the relation of cause and effect. To use a very familiar example: Suppose you pass a piece of ground where to your knowledge there stood but a very few weeks before a heavy growth of timber and observe that the trees are gone. If you see piles of freshly sawed lumber, you can argue that the trees have been cut by man; if on the other hand you see bent and torn trees, you can as surely reason that a cyclone has visited that neighborhood. In each case you argue from effect back to cause. This seems very simple, but is often a very treacherous argument, for the alleged cause may be entirely inadequate or may be so involved with other unrecognized causes that the deduction you make is not warranted. You must examine the connection very carefully and make sure that it is acausalrelation and not acasualone.
Argument from Resemblance.—Then there is the argument from resemblance, which is simply another form of causal relationship. The argument, for example, would run that conservation must surely be a good thing for the United States because it was a good thing for New Zealand. That conclusion is sound if the conditions in the two countriesare the same, but not otherwise; and it is upon this rock of difference in conditions that arguments from resemblance so often split. Watch them. The same rule may not apply to reforestration in Idaho as in Maine, for instance, because conditions are dissimilar in many respects.
If you carefully study these forms of argument, and can estimate the value of opinions and circumstantial evidence, you will not only be able to build up a bomb proof argument of your own but you will be able to detect fallacies in your opponent’s discussion. When you have mastered the one branch of the case you are equipped to meet the other, for the two are identical.