RI Critical Thinking Unit G (Fallacies) 2023

UNIT G Fallacies

FALLACIES ▪ Definition: a fallacy is a type of incorrect argument that may seem to be correct but actually isn’t ▪ Note: not all mistaken arguments are fallacies; only typical errors are fallacies.

FORMAL FALLACIES ▪ Two formal fallacies: ▪ 1) Affirming the Consequent ▪ 2) Denying the antecedent ▪ They look valid but they aren’t

AFFIRMING THE CONSEQUENT ▪ Structure: P1: If p then q P2: q C: p (P1-2) ▪ This is not to be confused with modus ponens ▪ Problem: ignores the possibility that there are other conditions apart from P that might lead to Q ▪ Example P1: If there is a traffic jam, a colleague will be late for work P2: A colleague is late for work C: He was caught in a traffic jam (P1-2) ▪ But he could have a faulty alarm clock ▪ Note: if P1 is changed to “q iff./only if p”, then no fallacy

INVALID OR STRONG? P1: If it rained last night, then the streets are wet this morning. P2: The streets are wet this morning. C: it rained last night. (P1-2) ▪ Looks like affirming the consequent ▪ But did the author intend a deductive argument? ▪ Probably not. ▪ If not, then it is (inductively) strong ▪ Note: always check if an invalid argument is actually strong

DENYING THE ANTECEDENT ▪ Structure: P1: If p then q P2: Not p C: Not q (P1-2) ▪ This is not to be confused with modus tollens ▪ Problem: some alternative explanation/cause might be overlooked ▪ Example P1: If there is a traffic jam, a colleague may be late for work. P2: there is no traffic jam C: the colleague will not be late for work (P1-2) ▪ But his alarm clock could have stopped working

INFORMAL FALLACIES ▪ There are hundreds of such fallacies ▪ Here are some of the more common ones (more are in your lecture notes)

AD HOMINEM ▪ A.k.a. attacking the person ▪ A theory is discarded not because of any evidence against it or lack of evidence for it, but because of the person who argues for it. ▪ Example A: The Government should enact minimum-wage legislation so that workers are not exploited. B: Nonsense. Y ou say that only because you cannot find a good job.

AD IGNORANTIAM ▪ A.k.a. appeal to ignorance ▪ The truth of a claim is established only on the basis of lack of evidence against it. ▪ Example Arguing that unicorns exist because there is no evidence against such a claim. ▪ Note 1: At first sight it seems that many theories that we describe as scientific involve such a fallacy. ▪ E.g.: the first law of thermodynamics holds because so far, there has not been any negative instance that would serve as evidence against it. ▪ But here, there is positive evidence for the scientific law ▪ Note 2: where there are only 2 rival claims, the falsification of one claim (C1) without evidence for/against the other claim (C2) is sufficient to establish C2.

AD POPULUM ▪ A.k.a. appeal to popularity ▪ The truth of a claim is established only on the basis of its popularity and familiarity. ▪ Commonly seen in commercials ▪ Example P1: Commercial says that X is t