Concept · Cognitive Bias: Informal fallacies of ambiguity
Ambiguous middle term
Origin: Traditional syllogistic logic
Biological Parallel
'Successful organisms are adapted. Adapted organisms survive. Therefore, successful organisms survive.' Circular—because 'adapted' and 'successful' mean the same thing (survival/reproduction). The ambiguous middle term shifts meaning: adapted-as-trait vs adapted-as-outcome. Evolutionary biology wrestles with this constantly: 'fitness' connects genotype to phenotype, but the term's meaning shifts subtly. Is fitness a property (robustness) or an outcome (reproductive success)? Ambiguous middles make tautologies look like explanations.