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Reasoning Lab
Take arguments apart. Test their support. Repair their weaknesses. Build and stress-test definitions. Construct formal proofs. 18 tools, all free, all designed to teach the skill — not just produce the output.
How students use these together
The tools fit four natural workflows. You don't have to follow them in order — but each chain is a coherent practice from start to finish.
Decompose a passage into premises and a conclusion, render it in standard form, then visualize the inferential structure.
Check for known fallacy patterns, evaluate the support relation across premises, then rewrite the argument as the strongest version of the underlying claim.
Construct a definition from class plus distinguishing feature, then stress-test it against examples, non-examples, and borderline cases.
Verify what a propositional formula is, then use natural deduction to derive what follows from premises with semantic per-rule checking.
Take arguments apart
Pull an argument apart and see its inferential structure. Useful for any passage where the structure isn't obvious from the prose order.
Paste a passage; identify the premises and conclusion. The tool flags indicator words and runs structural sanity checks.
Open tool →Convert an ordinary-language argument into a clean numbered standard-form layout. Mark implicit premises explicitly. Copy to clipboard.
Open tool →Diagram premises, sub-conclusions, and the main claim with a node-and-arrow map. See what supports what.
Open tool →Evaluate arguments
Check whether the premises support the conclusion, and whether the inference matches a known pattern of bad reasoning.
Check an argument against 14 common fallacy patterns with transparent heuristics. Surfaces possible matches with the evidence that triggered them — judgment stays with you.
Open tool →Per-premise relevance ratings plus across-the-set sufficiency evaluation. Keeps the two judgments visually distinct and feeds back structured repair suggestions from your own ratings.
Open tool →Compute the posterior probability of a hypothesis from a prior and two likelihoods. Reports the Bayes factor, a plain-English strength band, the worked calculation, and a focused callout for the base-rate-neglect / mammography-paradox case.
Open tool →Score the structural strength of an inductive generalization or analogical argument on four objective criteria. Identifies the weakest criterion and suggests where to focus repair. Pedagogically distinct from Bayesian updating: this scores the form, not the numbers.
Open tool →Three-stage walkthrough for IBE: list observations, propose competing explanations, score each on five fixed criteria (Scope, Power, Simplicity, Coherence, Testability). Computes which is best supported and flags the 'explains everything' trap, narrow margins, and weak fields.
Open tool →Apply John Stuart Mill's five methods of causal inference (Agreement, Difference, Joint, Concomitant Variation, Residues) to a case-table of candidate factors and observations. Identifies which factors satisfy each method's structural criterion.
Open tool →Repair arguments
Take a weak, unclear, or fallacious argument and rewrite it into the strongest charitable version that the underlying claim supports.
Work with definitions
Construct and stress-test the concepts your arguments rest on. Many weak arguments rest on unclear terms.
Walk through the genus-differentia decomposition (in plain English), assemble a draft definition automatically from the parts, then check it against 10 common definition problems.
Open tool →Run a definition against examples, non-examples, and borderline cases. Eight tests (A-H) surface defects from the patterns of mismatch between expected and actual verdicts.
Open tool →Use formal logic
Symbolic tools for evaluating propositional formulas, building natural-deduction proofs with per-rule semantic verification, and visualizing categorical claims.
Generate truth tables for any propositional formula. Detects tautologies, contradictions, and contingent statements. Compare formulas side by side.
Open tool →Natural-deduction proof builder with semantic per-rule checking — the validator parses your formulas and verifies the cited lines actually license the move you named.
Open tool →Two- and three-circle Venn diagrams for visualizing set relationships and basic categorical claims. Useful before working with formal A/E/I/O notation.
Open tool →Check the validity of any categorical syllogism. Identifies figure, mood, and standard name (Barbara, Celarent, …); reports validity under both modern and traditional Aristotelian interpretation; flags exactly which of the five rules is violated when invalid.
Open tool →Pedagogical companion to the Syllogism Checker. Enter one categorical statement; see whether its subject and predicate are distributed, with a learner-facing explanation of why and a side-by-side reference table for all four AEIO forms.
Open tool →Explain concepts
Step-by-step animated walkthroughs of the central concept in each reasoning track. Use as a quick refresher before practice or as a primer before starting a unit.
Roadmap
18 tools live today; 9 more are planned across the next two phases. Each one is being built to the same rigor bar as the existing suite — no fake functionality, no AI grading masquerading as judgment.