III. Fallacies of causal relation.
We have already considered the importance of causal relation in argumentation. A relation clearly established between a cause and an effect affords a substantial basis for valid reasoning. The failure to establish such relation results in error. Of course the causal relation may exist although undiscovered. Nevertheless, the failure to show such relation should always be considered as a warning to look out for fallacies.
1. Fallacies of the argument from effect to cause.
The argument from effect to cause may be shown to contain a fallacy by proving any one of the following contentions:
1. That the alleged cause was not sufficient to produce the effect.
2. That an independent cause intervened between the alleged cause and the effect.
3. That the alleged cause was prevented from operating.
In arguing from a known effect to an unknown cause certain fallacies occur with such frequency that we must give them special attention. Of these common errors the following are the most important:
(1). Mistaking coincidence for cause.
Most superstitions are due to this fallacy of mistaking coincidence for cause. A black cat crosses our path as we are starting out on a journey. If some misfortune overtakes us before our return our minds immediately revert to the old superstition that if a black cat crosses our path we must turn back and make a fresh start if we wish to ward off disaster. The black cat is regarded by the superstitious as the cause of the disaster. Obviously there is no causal relation between the appearance of the black cat and the occurrence of the disaster. It is merely a coincidence. If we regard it in any other light we are mistaking coincidence for cause.