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A complete logic curriculum
Lessons that teach you to build proofs, weigh evidence, and spot bad arguments — with instant AI feedback on every response you write. Start free. Student Pro from $14/month or $119/year.
Built for serious students and instructors who want more than quiz apps
Cross-modal reasoning
Most logic courses only teach one kind of thinking: the strict “if A, then B” kind. But most everyday arguments don't work that way. You generalize from examples. You pick the likeliest explanation. You update when new evidence comes in.
Each of those is its own skill with its own standards. We teach them on their own terms, then show you where they connect.
Formal Systems
Start with if-then statements and truth tables. Build up to syllogisms, full quantified proofs, and line-by-line natural deduction. The structural core underneath every argument you'll evaluate later.
How it works
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Each lesson walks you through the ideas with careful exposition, worked examples, and formalization patterns, not just a list of rules to memorize.
2
Write proofs, construct explanations, evaluate arguments, and get AI-powered feedback that tells you exactly where your reasoning breaks down.
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Progress tracking across 69+ lessons and 14 units shows you what you know, what needs work, and what to study next.
Inside the product
A peek at three things most "logic" learning apps don't actually do. You won't see these anywhere in a multiple-choice textbook flashcard deck.
Derive Qa from ∀x(Px → Qx), Pa
Line by line, with the rule you used. The system checks your justifications and tells you when a step doesn't follow — not just whether the final answer is correct.
Every concept you practice gets scheduled to come back right before you'd forget it. It's the same algorithm that keeps language-learning apps honest, applied to reasoning.
Why Rigorous Reasoning?
Every unit starts with the idea, walks through a worked example, then hands you practice. You never guess at what you're supposed to know.
Deduction is one tool. You'll also learn inductive generalization, inference to the best explanation, and Bayesian reasoning — and how they all fit together.
Historical context. Explicit rules of inference. Mastery checks that tie units together. This is a curriculum, not a pile of flashcards.
Pricing
Start with free access to sample lessons. Unlock the full curriculum, AI feedback, and progress tracking for $14/month or $119/year.
Full curriculum
Search by topic, track, concept, or lesson name. Every card previews what's inside before you open it.
Foundations
5 lessonsWhat reasoning is and why structure matters
Students learn what arguments are, how to identify their parts, distinguish three fundamental modes of reasoning, evaluate argument quality, spot arguments in everyday language, and understand why formalization is valuable.
Inside This Unit
Definitions And Concepts
4 lessonsHow to construct, classify, and evaluate definitions rigorously
Students learn what definitions do, how different kinds of definitions serve different purposes, and how to assess definitions for scope, circularity, vagueness, and practical usefulness. The unit equips learners to both build better definitions and critique sloppy ones.
Inside This Unit
Natural Deduction
5 lessonsWhy some conclusions follow necessarily
Students learn to distinguish validity from truth, translate ordinary arguments into symbolic form, construct short natural-deduction proofs, and diagnose exactly where a flawed derivation breaks down.
Inside This Unit
Categorical Logic
6 lessonsHow class statements support traditional deductive reasoning
Students learn to analyze standard-form categorical propositions, master quantity and quality, use the square of opposition, represent class claims with Venn diagrams, map syllogisms by major/minor/middle terms, and evaluate categorical syllogisms by distribution rules and diagrammatic tests.
Inside This Unit
Propositional Logic
6 lessonsHow whole statements combine into logically assessable structures
Students learn to identify atomic and compound statements, master the five connectives of propositional logic, symbolize natural-language arguments, evaluate validity with truth tables, and construct formal proofs using basic inference rules.
Inside This Unit
Predicate Logic
5 lessonsHow internal sentence structure changes formal reasoning
Students move beyond sentence-level structure to analyze internal form with predicates, variables, and quantifiers. They learn to translate quantified claims, manage quantifier scope and variable binding, and construct short proofs using universal and existential instantiation and generalization.
Inside This Unit
Modal And Intensional Logic
5 lessonsReasoning about what must, might, and could have been
Students learn to reason about necessity, possibility, and counterfactual conditionals using the box and diamond operators, possible-world semantics, and the Lewis-Stalnaker treatment of would-conditionals. They also learn to formalize de dicto and de re modal claims and to apply modal reasoning to philosophical, ethical, and scientific arguments.
Inside This Unit
Fallacies And Errors
5 lessonsFrom fundamental inferential failures to specific species across modes of reasoning
Students learn a systematic framework for fallacies by grouping common errors under fundamental patterns of reasoning failure, then tracing how those patterns generate distinct species in deductive, inductive, abductive, best-explanation, Bayesian, and problem-solving contexts. The unit emphasizes diagnosis and repair rather than label memorization.
Inside This Unit
Inductive Logic
5 lessonsHow to reason well under uncertainty
Students learn how inductive reasoning differs from deductive reasoning, how to measure inductive strength, and how to assess generalizations, analogies, and causal claims responsibly. The unit builds from the idea of defeasible support through sampling, analogy, and Mill's methods for disentangling causation from correlation.
Inside This Unit
Bayesian Probability
4 lessonsHow priors, likelihoods, and evidence interact in rational belief revision
Students learn the logic of Bayesian reasoning, including priors, likelihoods, posterior updating, base rates, and the disciplined use of probabilistic evidence in inquiry and decision making. The unit emphasizes qualitative Bayesian discipline first and then builds toward simple quantitative updates.
Inside This Unit
Abductive Logic
5 lessonsHow to compare explanations without confusing them with proofs
Students learn how arguments to the best explanation work, how to compare competing hypotheses using explanatory virtues, and how to state abductive conclusions with the right level of confidence. The unit emphasizes that abduction is a comparative discipline, not a search for single winning stories.
Inside This Unit
Problem Solving Logic
4 lessonsHow to reason from a problem state to a workable next move
Students learn to formalize practical problems, identify goals and constraints, compare candidate strategies, and justify a plan of action without pretending that every problem has a single certain answer. The unit builds from problem analysis through strategy selection to disciplined revision under new information.
Inside This Unit
Decision And Rational Choice
5 lessonsHow rational agents choose when outcomes depend on chance
Students learn the logic of rational decision making under risk and uncertainty, including expected value, utility, decision matrices, dominance, and the systematic biases that cause real decisions to depart from the normative ideal. The unit builds from qualitative preference reasoning through quantitative expected-utility analysis to the integrated evaluation of complex real-world choices.
Inside This Unit
Mathematical Foundations
5 lessonsThe mathematical scaffolding that makes formal reasoning possible
Students learn the language of sets, relations, and functions that underlies most of modern formal logic. They master set operations, relational properties, equivalence classes, partitions, order relations, functions, cardinality, and the pigeonhole principle, and they use set theory as the semantic foundation for categorical and predicate logic.
Inside This Unit
Not sure where to start?
Ten quick reasoning questions. See your strengths and gaps across deduction, induction, probability, and more — then get personalized unit recommendations.
Free to start. Your first lesson is one click away.
Create free accountReasoning Under Uncertainty
Most real arguments don't strictly prove their conclusions — they support them. You'll learn how to generalize from examples, pick the best explanation when multiple are possible, and update your beliefs as new evidence comes in. Each tool with its own standards.
Conceptual Control
Spot the fallacies that keep showing up in bad arguments. Write definitions that hold up under pressure. Work through problems when you're stuck. The skills that connect formal logic to the arguments you meet in real conversations.
When you've mastered something, the app tells you to skip ahead. When you're stuck, it sends you to focus practice. Nobody has to waste lessons on ground they've already covered.