Argumentum ad ignorantiam

An argument from ignorance is a type of reasoning where a premise is considered true because it has not yet been proven otherwise. The speaker could, for example, claim that aliens visit our planet and abduct farmers because it has never been conclusively shown not to happen. However, as it is phrased on the Secular Web [2], “In scientific investigation, if it is known that an event would produce certain evidence of its having occurred, the absence of such evidence can validly be used to infer that the event didn’t occur.” What follows is that proof should be produced to support the claim that aliens do visit our planet and disturb the status quo; not the other way around. No implants, alloys, spaceship parts, body tissues, artifacts, or even persuasive photographs have ever been presented.

Argumentum ad nauseam

Certain arguments are thought to gain plausibility when they are restated over and over again. Such is the case with the argument from repetition. The speaker – and supposedly the audience – will consider the argument more valid if it is restated more often than opposing views [3].

Any major religion based on sacred texts can serve as an example here. The longer a given system of beliefs functions, the more apologists emerge, and the more literary works about it are written. Consequently, ancient faiths have hundreds and thousands of manuscripts, books, essays, comments, and pamphlets supporting them. However, all these papers are supposedly based on a limited number of scriptures, which means that – without any newer revelations – they restate the existing ones.

Argumentum ad numerum

This argument is based on the number of people who already believe a proposition to be true; it is also otherwise known as argumentum ad populum – an argument appealing to the popular opinion of the audience. For example, a Gallup poll released in 2019 [4] suggests that, at the time, 40% of respondents believed evolution through natural selection to be a false explanation of human origins. On the other hand, 22% believed in the evolutionary origins of Homo sapiens (though it would be more accurate to say that 22% understood the evolutionary process, since it is the only model with a solid scientific basis). Someone could conclude that 40% of the population cannot be wrong, and therefore evolution is disproved. This is not the case, if only because the theory of evolution has already managed to predict certain scientific discoveries and does not require the acceptance of the general public to do so [5]. It is, in other words, extremely unlikely to be false at the present moment of scientific development.

Argumentum ad numerum is often accompanied by argumentum ad antiquitatem, which supposes that certain beliefs have existed for so long that they must be true. This argument can be easily refuted if we consider, for example, for how long humanity believed that the Earth was the center of the universe or that it was flat. To be fair, there are still people believing the Earth to be a flat disc, and the prolonged existence of their opinion clearly doesn’t validate it.

Conclusion

Dealing with logical fallacies is an everyday chore for anyone who follows media outlets, takes part in online debates, or simply wants to learn. Political and ideological divisions in the XXI century are as strong as ever and require skeptical and logical tools to properly distill information. Misinformation and propaganda are usually disguised in seemingly sound argumentation, but a properly armed skeptic should have no problem sifting it out.