Internal Evidence, The Fallacy of

The error of judging a proposition to be true on the strength of evidence selected, intentionally or unintentionally, to confirm it. This is related to Cognitive Dissonance and Begging the Question, and to forms of Expertise (the No Evidence Fallacy).

In some cultures it is safe to assume that statements which are intended to be believed are in fact true, but this state of affairs is easily eroded and lost. In its absence, the other option—when arguing a case which you are sure is right—is to meddle with the evidence to suit your case. This can help to persuade your victim, and yourself, but with some strange results.

One of the reasons why strange beliefs are so addictive is that they cannot easily be faulted by internal evidence. If you allow yourself to forget everything else you know about a subject, and listen with rapt attention just to the story itself, the question of whether it is true or not does not even seem to arise. Here, for instance is Oliver Goldsmith (1730–1774), doctor, playwright, essayist, naturalist, writing about a patient (not one of his own) from a farming family that lived in such close and loving association with their cows that they became like them:

The man in question was a citizen of Bristol, of about 20 years of age, and what seemed more extraordinary still, of a ruminating family, for his father was frequently subject to the same infirmity. This young man usually began to chew his meat over again within about a quarter of an hour after eating. His ruminating after a full meal generally lasted about an hour and a half, nor could he sleep until this task was performed. The victuals, upon return, tasted even more pleasantly than at first; and returned as if they had been beaten up in a mortar. If he ate a variety of things, that which he ate first came up again first; and if this return was interrupted for any time, it produced sickness and disorder, and he was never well till it returned. Instances of this kind, however, are rare and accidental; and it is happy for mankind that they are so. Eating is a pleasure of so low a kind, that none but such as are nearly allied to the quadrupede, desire its prolongation.^I80

This is from the man who gave us:

Sweet was the sound, when oft at evening’s close
Up yonder hill the village murmur rose.^I81

Admittedly, it is an extreme case, but it illustrates the possibility of sustaining a ridiculous proposition simply by referring to more and more circumstantial evidence: your life can be given meaning and passion by persistent invention, and your friends are those who see it the same way. There is no argument so absurd that it is impossible to find abundant evidence in its support.

A reliable source of convenient truths is the existence of sharply distinct factions, each on the defensive. And once you are in a group united by a strong opinion—a faction—it is hard, bordering on impossible, to think independently. If you do, you are likely to be excommunicated, losing the meaning of your life, including your friendships; to help you to stay in line, there are little mantras (“global justice”, “the liberation of humanity”) around which, or against which (“imperialism”, “profit”, “greed”), you can unite.

Here is a large-scale farmer mixing up exaggeration, fiction and outrage at a tendency he evidently detests: the “Organic Taleban”, he writes, want us to believe that organic fertilisers are “made by little old Cornish ladies boiling up seaweed on the beach”. Well, he does not really believe that; it is chortling hyperbole, but he does believe that organic cultivation is no less absurd. He is, however, well-defended by the faction of those who couldn’t agree more.^I82

Related entries:

Relevance, Expectations, Memory Fillers, Imagination, Generalisation Fallacies.