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Week 4 · Module overview

Week 4 — Conditionals and Deductive Forms

Critical Thinking Free sample edition

Welcome to your Week 4 Start Here page.

Why this matters

A nursing student reading a dosing rule and a business major reading a refund policy both need to know what an if sentence requires and what it promises.

In plain language

This week is about "if" sentences, the kind that run parking rules, refund policies, and course requirements. You will learn to read a conditional (an "if, then" claim) by naming its two parts and the one situation that makes it false. You will meet four patterns of reasoning that never fail, the valid forms (patterns where true reasons always bring a true conclusion), and two look-alike patterns that do fail, the formal fallacies (invalid patterns, whatever the topic). You will also learn to tell a rule's necessary condition (something that must be true) from its sufficient condition (something that is enough on its own). Misreading an "if" sentence is one of the most common reasoning slips there is, and this week gives you the tools to catch it.

  • Already covered: Week 3 taught you validity and the counterexample method.
  • This week: conditionals, the valid forms, and the two formal fallacies.
  • How they connect: you test each form with a counterexample.
  • Where we're going next: Week 5, Categorical Reasoning.

Focus

What does an if sentence promise, and which arguments built on it really hold?

By the end of this module, you should be able to:

  • [ ] rewrite "only if" and name a conditional's two parts
  • [ ] name the four valid forms and the two formal fallacies
  • [ ] refute a formal fallacy with one counterexample
  • [ ] tell necessary from sufficient, and converse from contrapositive

To-do

Plan your week

  1. Read Chapter 4 (about 40 minutes), then the lecture and slides.
  2. Work the lecture tutorial (60–90 minutes) and the practice set (about 20 minutes).
  3. Do the Argument Workshop (about 90 minutes), the discussion, and the assignment.
  4. Take the quiz.

This week's checkpoint: explain why a wet field does not prove it rained, using the sprinkler case.

You've got this

Take it in order, and ask your instructor if a step snags.

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