“Either you subscribe to the journal or you don’t. Your subscription lapsed, and therefore you don’t subscribe to the journal.”
The fallacy of false dichotomy is that the either/or premise is false if more than two choices exist. Therefore the conclusion is invalid:
“Either the hypothesis is proved or disproved. This experiment did not prove the hypothesis. Therefore it must have disproved it.” Unfortunately, science is almost always less efficient than this. Experiments may support hypotheses, refute them, or disprove them, but never prove them.
False dichotomy is frequent among the general public.
Sometimes one premise and the conclusion are obvious and unstated:
“Either make at least 100 measurements or skip the experiment entirely.” The premises (P) and conclusion (C) are: P1: the experiment is worthless if <100 measurements are made; P2: surely you want the experiment to be worthwhile; and C: therefore you will want to do at least 100 measurements.
- Suppressed evidence is the omission of evidence that weakens or fatally undermines one premise. This fallacy is frequent among both lay people and scientists. Few scientists deliberately hide an assumption. Instead, they may suppress evidence passively, by an unconscious ‘forgetting’ or by a conscious decision that the evidence is too flawed to warrant mention. A different, but related, lapse of objectivity is the ignoring of evidence that leads to a competing conclusion.
- Ambiguity creates a fallacious argument, when misinterpretation of an ambiguous premise results in a wrong conclusion. Usually the ambiguity arises from punctuation or grammar and is merely a temporary distraction while reading a publication:
“We analyzed our experiments on monkeys using multivariate statistics.” Smart monkeys!
Misinterpretation of someone else’s ambiguously stated premise is more serious. People often are unaware of ambiguities in their own statements, because of familiarity with the subject. Others then misinterpret the statement, leading them to incorporate it into an argument that is doomed by the incorrect premise.
A sign on a beach says, “Sharks! No swimming!” [Ennis, 1969]
My colleagues and I have often succumbed to the fallacy of ambiguity in interpreting telexes. The sender cannot foresee the ambiguity that cost-saving brevity has introduced. For example: “. . . STOP MISS YOU STOP LOVE END”
- False cause is an argument in which a relationship is incorrectly assumed to be causal. Several types of associations can be misinterpreted as causal: (1) one event may precede another and become misidentified as its cause; (2) the cause may be confused with the effect if the two are nearly simultaneous; (3) a variable may control two others and thereby give those two an indirect association; and (4) the apparent association may be coincidental. Determining causality and dodging the potential pitfall of false cause are fundamental aspects of science. They are discussed in more detail in Chapter 3.
