Welcome to Logic, Fallacies & Bias Mastery! You're about to build a powerful thinking toolkit that will help you spot bad reasoning and make better decisions every day.

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Ready to become a clear-thinking detective?

Let's start with deductive logic - the gold standard of reasoning. In deductive logic, if your starting points are true, your conclusion must be true too. No exceptions.

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Think of it like mathematical proof; can you think of a simple math example where this works?

Here's why this matters: every day you make decisions based on reasoning. "If it's raining, I'll get wet without an umbrella. It's raining. Therefore, I need an umbrella."

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Which statement in that umbrella example was the premise, and which was the conclusion?

Deductive arguments have a specific structure: premises (your starting facts) lead to a conclusion. When the structure is valid and premises are true, you get rock-solid reasoning.

Let's look at the most common valid form: "If A, then B. A is true. Therefore, B is true."

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Can you create your own quick example that fits this exact pattern?

This pattern is called modus ponens (Latin for "affirming by affirming"). Here's a simple example:

If you study hard, you'll pass the test. You study hard. Therefore, you'll pass the test.

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Can you spot the "If A, then B" part and the conclusion?

The beauty of modus ponens is its reliability. Whenever you see this pattern and the premises are true, the conclusion must be true.

You'll find this pattern everywhere - in science, law, everyday decisions, and even arguments with friends!

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Where have you recently seen this pattern used—at work, in the news, or elsewhere?

But here's the key: the structure must be exactly right. Even small changes can make an argument invalid, even if it sounds convincing.

We'll practice identifying when arguments follow valid patterns versus when they just sound good but aren't logically sound.

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What's one argument you've heard that sounded right but later proved logically flawed?

Type

Multiple Choice

Practice Question

Let's identify a valid modus ponens argument. Which of these follows the correct "If A, then B. A is true. Therefore, B is true" pattern?

A. If it rains, the ground gets wet. The ground is wet. Therefore, it rained. B. If it rains, the ground gets wet. It is raining. Therefore, the ground gets wet. C. If it rains, the ground gets wet. It's not raining. Therefore, the ground won't get wet. D. The ground is wet, so it must have rained.

Suggested Answers

• A
• B - Correct
• C
• D