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11. Informal Fallacies - Relevance Part 3

 

Summary​

This is the third of four sessions on the fallacies of relevance, turning to attempts to distract and especially inappropriate authorities, fallacies that substitute some "authority" for reasons actually relevant to the truth. Five are covered.

Consensus gentium (appeal to the majority)​

"Agreement of the people", arguing that something is true because most people believe it. (This concerns how many believe, distinct from the ad populum.) The truth of a claim never depends on how many accept it. Examples: "nearly everyone reads the Bulletin"; "you should believe in God because most of the world does"; "50 million freshmen can't be wrong."

Argumentum ad ignorantiam (appeal to ignorance)​

Claiming X is true because it has not been proven false (or false because not proven true). Lack of evidence is not evidence, and the burden of proof normally falls on whoever makes the affirmative or weightier claim.

Important exceptions: absence of evidence can support a conclusion when evidence would be expected to surface after a careful, extensive search, e.g. looking under the bed for a dog, scientists failing for decades to detect the luminiferous ether (inductively strong evidence it doesn't exist). There is also the legal standard: if nothing is proven beyond a reasonable doubt, the jury must acquit. (The shift on King David's historicity after the 1993 Tel Dan stele shows how new evidence flips such arguments.)

Argumentum ad verecundiam (appeal to authority)​

Citing an authority in place of an argument. This is not inherently fallacious, most of what we know we accept by trusting legitimate authorities, and deferring to an expert consensus within its field is often wise. It becomes an illegitimate appeal when the authority is:

  • irrelevant (a movie star on politics) or in the wrong field (a physicist on tax law);
  • unreliable, biased, or prejudiced;
  • unnecessary (a clearer direct argument exists, e.g. simply demonstrating Euclid's theorem);
  • dogmatic (claiming certainty rather than probability); or
  • uncritical (ignoring genuine debate and disagreement among authorities).

Rejecting a consensus is rationally defensible if you can both explain the consensus on sociological/philosophical grounds (not the genetic fallacy, this questions the appeal, not the origin) and offer a rigorous alternative. The core point: no statement is true because of who said it, only because it corresponds to reality. Rational people can reach different conclusions from the same facts due to different presuppositions.

Argumentum ad futurum (appeal to the future)​

Basing an argument on hoped-for results that have not yet occurred, treating non-existent future evidence as if it counted now: "embryonic stem-cell research will one day cure paralysis, so we should continue"; "a one-world government is best because it will produce peace."

Wishful thinking​

Arguing that something is true simply because you want it to be, or because it would be "cooler" or "more liberating" to believe. As with appeals to emotion, truth has nothing to do with our desires.

Where this leads​

This wraps up the appeals to authority. The next (fourth) relevance session covers the diversion category of distractions, after which the course still has the entire presumption family to cover.