What is the fallacy of excluding counterexamples?

Question

What is the fallacy of making up new categories so as to exclude counterexamples which falsify the rule?

Thank you for any example from the academic literature.

Answer 1

When deployed improperly, this is the informal fallacy, "no true Scotsman":

one modifies a prior claim in response to a counterexample by asserting the counterexample is excluded by definition.

The original category gets modified by a term like "real," "true," etc.

Of course, refinement and subdivision of categories over time can also be an acceptable means of organizing entities. This is the basis behind morphological classification of species.

Answer 2

It's not a fallacy at all, and you can't get by without it. It's fixing a problem in the definition or communication of a concept.

Alice: "The English word colour has a letter u."

Bob: "Well, Americans..."

Alice: "Oops, you're right: the British English word colour has a letter u."

or:

"Oh, I meant English as in belonging to England not English as in the language English."

or even:

"Silence, colonial scum! Filthy Americans aren't true English speakers! Speaking English means speaking it the way they speak it in England, and in England it has a letter u."

All perfectly fine (rationally speaking). Alice is just clarifying what she meant.

No True Scotsman is carrying on against the evidence as if the initial claim did not need modification, while in fact modifying the initial claim. It is a kind of dishonest (or self-deluding) rhetorical tactic. It's an informal fallacy if the speaker accidentally tricks himself into thinking that the initial claim really didn't need modification or clarification.

As with all informal fallacies, the only use for its name, ever is as an indexing point to help yourself avoid making certain cognitive errors in your own internal reasoning. This error in particular is usually trivially averted in actual conversation.

---

Useless:

Alice: "X is like this."

Bob: "Y is not like this and is called an X."

Alice: "Y is not a true X."

Bob: "NO TRUE SCOTSMAN!"

Alice: "STYLE OVER SUBSTANCE!"

Bob: "EXPELI ARMUS!"

Alice: "AVADA KEDAVRA!"

---

Useful:

Alice: "X is like this."

Bob: "Y is not like this and Y is an X."

Alice: "Y is not a true X."

Bob: "Okay, what is your definition of a true X and a false X?"

Alice: "A true X is [whatever]."

Bob: "I was talking about X meaning [whatever else]."

Answer 3

The phenomenon you mentioned is rather common in Academia. Lakatos in his book Proofs and Refutations referred to it as "monster-barring". There is a considerable literature discussing this; see e.g.,

Leopold Karl.

Here is a pair of examples:

1. The whole machinery of sigma-algebras was developed to monster-bar the phenomenon of nonmeasurable sets. One would have naively expected to be able to assign a reasonable (Lebesgue) measure to every set. This is indeed possible if one sticks with ZF+(dependent choice), namely in the Solovay model. But generally dependent choice is not enough to some some important pieces of mathematics, such as the Hahn-Banach theorem. At this point one has no choice but to forego the totality of the measure, and reconcile oneself to working in a sigma-algebra of measurable sets.

2. Cauchy published a sum theorem in 1821 that amounts to the claim that a convergent series of continuous functions has a continuous sum. This is often reported in the literature as "Cauchy's mistake". However, in 1853 Cauchy modified the hypothesis of the theorem by including a "monster-barring" condition that is difficult to understand from the viewpoint of non-infinitesimal analysis. It is easier to understand from the viewpoint of infinitesimal analysis; see e.g.,

Bascelli, T.; Błaszczyk, P.; Borovik, A.; Kanovei, V.; Katz, K.; Katz, M.; Kutateladze, S.; McGaffey, T.; Schaps, D.; Sherry, D. "Cauchy's infinitesimals, his sum theorem, and foundational paradigms." Foundations of Science 23 (2018), no. 2, 267-296. https://doi.org/10.1007/s10699-017-9534-y, https://arxiv.org/abs/1704.07723, https://mathscinet.ams.org/mathscinet-getitem?mr=3803893

Answer 4

As other answers have pointed out, this is often not a fallacy and can be done appropriately and in good faith. It is sometimes referred to as "monster barring", but that is a valid technique that shows up often in math and sometimes in science. When done in bad faith and in a particular way though, it can result in the "No True Scotsman" fallacy which is well discussed in other answers.

I am providing a separate answer because I suspect you may be thinking of the informal fallacy of moving the goalpost. Moving the goalpost usually manifests as rejecting some form of evidence, including counterexamples, and demanding additional evidence, usually after it was at least reasonably believed that everyone had agreed on what type of evidence would be necessary. This is not a formal fallacy, but it is an informal one that appears frequently in politics and in discussions about conspiracy theories. Snopes has a rather good writeup of it at https://www.snopes.com/articles/464308/logical-fallacies-and-moving-goalposts/

Answer 5

I'm in the "not necessarily a fallacy" camp, as this move can be quite fruitful.

1. All numbers can be expressed as ratios of integers (Pythagoras or someone).
2. The square root of 2 cannot be expressed as ratios of integers (Hippasus of Metapontum or someone).
3. The square root of 2 is not a rational number.

This could have been a "no true Scotsman", but instead led to several centuries of fruitful work by Dedekind, Cantor, etc.

Answer 6

My hunches, if they mean anything at all:

1. Cherry-picking/Confirmation bias (ignoring counter examples)

2. Self-sealing argument (making ad hoc adjustments to a hypothesis so as to fit the facts, which isn't really bad if you consider the converse)

In sum, unfalsifiability and hence verging on or is pseudoscience (per Karl Popper)