Fallacies and Errors·Rules·Lesson 2 of 5

Deductive and Formal Fallacies

Examines fallacies driven by formal structure, quantifier scope, class reasoning, and invalid deductive patterns, and shows why these errors demand structural rather than evidential repair.

← Fundamental Fallacy Families Fallacies and Reasoning Errors Inductive, Abductive, and Best-Explanation Fallacies →

Student Pro

Unlock this lesson and the rest of the curriculum.

Free includes the entire Foundations unit plus the first lesson of every other unit. This lesson is in Fallacies and Reasoning Errors; the rest of the unit, and every other unit, is Student Pro.

In this lesson · 7 sections · 5 worked examples · 5 practice activities

What makes a fallacy formal
Conditional-form fallacies: affirming the consequent and denying the antecedent
Categorical and term-structure fallacies
Linguistic and scope fallacies: equivocation, amphiboly, and quantifier confusion
…and 3 more

$119/year

Under $10 a month, billed annually — or $14 month-to-month.

Every lesson in all 15 units
Unlimited detailed feedback on every written response
Full spaced-repetition queue and adaptive recommendations

Unlock with Student Pro Or $14/month

14-day refund on annual. Cancel anytime. No charge until you confirm at checkout. Already have Student Pro? Sign in.

Compare all plans Teaching a class? Team plans cover every student Back to Fallacies and Reasoning Errors Curriculum