Fallacies and Errors in the Wonderlands of Biology, Medicine, and Lewis Carroll

FALLACIES AND ERRORS IN THE WONDERLANDS OF BIOLOGY, MEDICINE, AND LEWIS CARROLL DWIGHT J. INGLE* "Contrariwise," continued Tweedledee, "If it was so, it might be: and if it were so, it would be; but as it isn't, it ain't. That's logic." He thought he saw an Argument That proved he was the Pope: He looked again, and found it was A bar of Mottled Soap. This is a review of kinds of fallacies and errors in inquiry and reasoning which are frequently accepted as plausible and of use in obtaining and judging evidence. I shall not discuss logical fallacies which violate the rules of syllogism , for they are used but little by researchers in biology and medicine. These are arguments which proceed from affirmation of the consequent or from denial of the antecedent, or they imply a logical connection where none exists. Strictly speaking, false assumptions and false information are not logical fallacies—they are called material fallacies because they have to do with facts—but they lead to insecure claims of proof and are listed here. It is commonly implied that a fallacy always leads to error. This is itself a fallacy. Fallacious reasoning sometimes leads to truth. There is no clearly defined line of demarcation between arguments which contain flaws and the most secure arguments that the researcher can construct. There are systems of formal logic which compel conclusions when the premises are valid, but this is not commonly true in fields of research where information is incomplete, where there are many sources of uncertainty [1], and where arguments involve inference. Both strong and weak arguments have each led to truth and to error, but the latter can be reduced when flawed reasoning is recognized and corrected. * Department of Physiology, University of Chicago. 254 I Dwight J. Ingle · Fallacies and Errors in Biology The review of fallacies in ordinary reasoning is never complete. The naming, definition, and classification of fallacies vary from one philosophic framework to another. It is not within my capacity to develop a logically secure treatment of fallacies. The following review goes only a little way toward classification. There remains a significant amount of overlapping of meanings of different fallacies. I have avoided the more subtle meanings of some fallacies, for I do not fully understand them. Although I wanted to illustrate each fallacy and error by an analogical example from the nonsense of Lewis Carroll [2, 3], I did not succeed and have included some quotations that are only reminders of the fallacies being described. Fallacies Which Assume That a Causal Connection Must Exist between Associated or Correlated Events The common error of judging guilt by association is related to this group of fallacies. Post hoc, ergo propter hoc (after this, therefore because of this).— This is to assume a causal relationship between that which has been done or has happened and that which follows. It is commonly judged that when a patient improves during therapy, the improvement was caused by the therapy. This is frequently true, but many diseases are self-limiting and improve with or without therapy. Suggestibility can affect the judgment of both the physician and the patient. Alice was glad to see that it revived him a good deal. "There's nothing like eating hay when you're faint," he remarked to her, as he munched away. The assumption of a cause-and-effect relationship between two associated events.—This is an extension of post hoc reasoning to the assumption that the occurrence of two or more events at the same time must have a causal connection. Both regular and accidental concomitances are bases of much folk medicine, folk lore, and superstitions . In physiology it has been assumed that the catabolic response to stress is caused by the accompanying rise in titer of circulating glucocorticoids, but it can be shown that the genesis of the catabolic response is more complex, for it will occur full-blown in adrenalectomized animals given a constant intake of glucocorticoids. Alice was very glad to find her in such a pleasant temper, and thought to herself that perhaps it was only the pepper that had made her so savage when they met...