If the argument stands the first test, the next question to ask is:—
(2) May some other cause intervene and prevent the action of the assigned cause?
During the spring of 1908 it was generally known that the Erie Railroad had no money with which to pay the interest that was about due on its outstanding bonds. Wall Street prophesied that the road would go into a receiver's hands. This result was extremely probable. Mr. Harriman, however, president of the Union Pacific, stepped in and by arranging for the payment of the interest saved the road from bankruptcy. This was an example of how an intervening cause prevented the action of the assigned cause. When Congress passed the Fifteenth Amendment to the Constitution, many people said that this legislation would inevitably cause the social, political, and financial ruin of the whole South. Since they did not take into consideration the intervening action of another cause, namely, drastic measures for negro disfranchisement by the white inhabitants of the South, their reasoning from antecedent probability was entirely erroneous.
2. ARGUMENT FROM SIGN.
ARGUMENT FROM EFFECT TO CAUSE. The process of reasoning from effect to cause is called argument from sign. Since every circumstance must be the result of some preceding circumstance, the arguer tries to find the cause of some fact that is known to exist, and thereby to establish the existence of a hitherto unknown fact. For instance, when one sees a pond frozen over, he is likely to reason back to the cause of this condition and decide that there has been a fall in temperature, a fact that he may not have known before. The sight of smoke indicates the presence of fire. Human footprints in the snow are undoubted proof that someone has been present.
In the following quotation, the recent prohibition movement in the South is said to be a sign that the voters wish to keep liquor away from the negro:—
What is the cause of this drift toward prohibition in the South? The obvious cause, and the one most often given in explanation, is the presence of the negro. It is said that the vote for prohibition in the South represents exactly the same reasoning which excludes liquor from Indian reservations, shuts it out by international agreement from the islands of the Pacific, and excludes it from great areas in Africa under the British flag; and that, wherever there is an undeveloped race, the reasons for restrictions upon the liquor traffic become convincing. [Footnote: Atlantic Monthly, May, 1908, p. 632.]
The strength of this kind of reasoning depends upon the closeness of the connection between the effect and the assigned cause. In testing argument from sign, one should ask:—
(1) Is the cause assigned adequate to produce the observed effect?
This test is precisely the same as the test of adequacy for antecedent probability. One could not maintain that the productiveness of a certain piece of ground was due entirely to the kind of fertilizer used on it, nor that a national financial upheaval was caused by the failure of a single unimportant bank. In each of these cases the cause suggested may have assisted in producing the result, but obviously it was not of itself adequate to be the sole cause.