Detecting Formal Fallacies in Rhetoric

A high school ELA sequence focused on identifying structural errors in reasoning. Students learn to distinguish between informal fallacies (content-based) and formal fallacies (structure-based), specifically mastering affirming the consequent, denying the antecedent, and the undistributed middle.

Logic Blueprints

Students distinguish between informal fallacies (errors in content/relevance) and formal fallacies (errors in the logical structure). They review examples to categorize errors based on whether the 'math' of the logic is broken.

The Result Trap

Students dive deep into the error of assuming that because a result occurred, a specific cause must have happened (If P then Q; Q; therefore P). They analyze forensic and medical scenarios where this error leads to false convictions or diagnoses.

The False Guarantee

This lesson examines the inverse error (If P then Q; Not P; therefore Not Q). Students look at political promises and advertising guarantees to see how this structure is used to mislead consumers.

The Penguin Paradox

Students analyze syllogisms where the middle term does not cover all members of the category, leading to false connections. They use Euler circles or diagrams to visualize why the connection fails.

The Speech Repair Shop

In this application lesson, students take text containing formal fallacies and rewrite it. They must alter the premises or the conclusion to make the argument formally valid, understanding the difficulty of maintaining truth while fixing structure.