Natural Deduction·Guided Practice·Lesson 4 of 5

Diagnosing Invalid Proof Steps

Students inspect flawed derivations and explain exactly why the steps fail, naming the mismatched condition of the rule being misused.

← Basic Natural Deduction Natural Deduction: Validity and Formal Proof Capstone: Building and Defending a Complete Deductive Argument →

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 Natural Deduction: Validity and Formal Proof; the rest of the unit, and every other unit, is Student Pro.

In this lesson · 7 sections · 5 worked examples · 2 practice activities

An invalid step is a specific rule failure
Wrong-direction conditional errors
Conjunction and disjunction misapplications
Scope violations in subproofs
…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 Natural Deduction: Validity and Formal Proof Curriculum