LogicalFallacies.org is a free, comprehensive guide to errors in reasoning — the logical fallacies and cognitive biases that quietly undermine arguments, decisions, and everyday thinking. Our goal is simple: to make flawed reasoning easy to recognize, so you can spot it in what you read and avoid it in what you write.
Alongside the reference, we build tools that read real text and name what's wrong with the reasoning — turning a library of definitions into something you can actually use on your own writing.
What we cover
The heart of the site is a plain-English reference to reasoning and its failures:
- Logical fallacies — every major fallacy, organized into formal and informal families, each with a clear definition and real examples. Short on time? Start with the common fallacies you'll actually run into most.
- Cognitive biases — a companion reference to the systematic ways our thinking skews, from confirmation bias to anchoring. Browse the full cognitive biases collection.
- Foundational explainers — the basics worth getting right, like what a logical fallacy is and what a syllogism is.
The tools
Free, AI-powered tools that analyze real text:
- Fallacy Detector — paste an argument and get every logical fallacy flagged and linked to its entry.
- Bias Checker — surface the cognitive biases shaping a piece of writing, yours or someone else's.
- Writing Lab — a full editor that scores your reasoning and flags fallacies and bias as you write, so you catch the weak spots before you publish.
- Fallacy Quiz — ten questions at the difficulty you choose, to find out how sharp your radar really is.
Who it's for
Anyone who wants to think more clearly and argue more honestly — students, analysts, debaters, and the simply curious. For people who write to persuade, The Writing Desk collects our guides on building arguments that hold up: how to find fallacies, edit for logic, and pressure-test a draft. For teachers, we offer lesson plans, worksheets, and classroom materials on our educator resources page.
Our approach
We favor plain language and concrete examples over jargon, and the collection is always under review — we add examples and sharpen explanations as the reference grows. The site is free to use; an optional Pro plan and a one-time Educator Pack support the work and unlock the full tools.
Get in touch
Have a question, a correction, or a suggestion for a fallacy or example we should add? We'd genuinely like to hear it. Reach us any time at support@logicalfallacies.org, or through our contact page.