The short answer
Logical Reasoning makes up two of the LSAT’s three scored sections. Each question gives you a short argument or exchange and asks one thing about it. The score reports in LSAC’s official practice platform group these questions into nine families: Conclusions and Disputes; Assumptions; Strengthen or Weaken; Flaws; Matching Flaws; Matching Structure and Principles; Deductions and Inference; Explain or Resolve; and Techniques, Roles, and Principles. Learning the families tells you what each question is really asking before you read the answer choices.
Below, each family is explained in our own words, with the narrower task names Think Clearly uses and the chapters that teach it.
| Family | Think Clearly task names | Chapters |
|---|---|---|
| Conclusions and Disputes | Main conclusion, Point of disagreement, Point of agreement, Complete the argument | 3, 9, 17 |
| Assumptions | Necessary assumption, Sufficient assumption | 11, 12 |
| Strengthen or Weaken | Strengthen, Weaken, Evaluate | 6, 13, 14 |
| Flaws | Flaw | 6, 7, 15 |
| Matching Flaws | Parallel flaw | 15, 16 |
| Matching Structure and Principles | Parallel reasoning, Principle (apply) | 12, 16 |
| Deductions and Inference | Must be true, Most strongly supported, Cannot be true | 4, 5, 10, 17 |
| Explain or Resolve | Explain a discrepancy | 14 |
| Techniques, Roles, and Principles | Argument role, Method of reasoning, Principle (justify) | 9, 12 |
1. Conclusions and Disputes
What it asks: what the author is trying to prove, or what two speakers actually disagree (or agree) about. Some versions ask you to supply the sentence that would finish the argument.
How to work it: find the claim every other sentence supports. Words like therefore help, but the test is the claim’s job, not its signal word. For a dispute, find one statement that one speaker would accept and the other would reject; a topic both mention is not enough.
Common traps: a premise offered as the conclusion (Wrong part), a conclusion stated more broadly than the author’s (Too strong), and a point only one speaker addresses.
In the book: Chapter 3, Arguments and support; Chapter 9, Conclusions, roles, and methods; Chapter 17, Disagreement, completion, and negative tasks.
Video lessons: watch free lessons on Conclusions and Disputes from teachers on YouTube.
2. Assumptions
What it asks: what the argument takes for granted. A necessary assumption is something the argument needs: if it were false, the argument would fall apart. A sufficient assumption is something that, added to the premises, would make the conclusion follow.
How to work it: name the gap between the evidence and the conclusion before you look at the choices. For a necessary assumption, negate the choice and ask whether the argument collapses. For a sufficient assumption, look for the missing link that makes the proof complete, even if it is stronger than needed.
Common traps: choices that would help but are not required (Too strong for necessary questions), and choices that repeat a premise (Already given).
In the book: Chapter 11, Necessary assumptions; Chapter 12, Sufficient assumptions and principles; Chapter 5, Conditional reasoning, for the logic underneath.
Video lessons: watch free lessons on Assumptions from teachers on YouTube.
3. Strengthen or Weaken
What it asks: which new fact would make the argument more or less convincing, or which information would be most useful to evaluate it.
How to work it: locate the weak link, usually an assumed cause, an unrepresentative sample, or a comparison of unlike things. A good strengthener closes the gap; a good weakener exploits it. Evaluate questions ask for the fact whose answer, one way or the other, would change your view.
Common traps: facts that are on topic but do not touch the inference (Irrelevant), and choices that push the wrong direction (Strengthens instead, Weakens instead).
In the book: Chapter 13, Strengthen and weaken; Chapter 14, Evaluate and explain; Chapter 6, Causes and alternative explanations; Chapter 7, Numbers, samples, and comparisons.
Video lessons: watch free lessons on Strengthen or Weaken from teachers on YouTube.
4. Flaws
What it asks: what is wrong with the reasoning. The answer describes the error in general terms.
How to work it: say the flaw in your own words first: treating correlation as cause, generalizing from a skewed sample, confusing a necessary condition with a sufficient one, shifting the meaning of a term, attacking the source instead of the argument, or treating a lack of evidence as proof. Then match the description to what the argument actually did.
Common traps: a real-sounding flaw the argument did not commit (Wrong flaw), and a description that overstates the error (Too strong).
In the book: Chapter 15, Flaws in reasoning, with Chapters 6 and 7 for causal and numerical errors.
Video lessons: watch free lessons on Flaws from teachers on YouTube.
5. Matching Flaws
What it asks: which answer choice contains an argument that makes the same mistake as the original.
How to work it: reduce the original to its skeleton and name its flaw. Check each choice’s conclusion first, then whether it commits the same error. A choice can share the topic and still have a different structure.
Common traps: same subject, different reasoning (Wrong structure), and a valid argument where you needed a flawed one.
In the book: Chapter 16, Parallel reasoning, building on Chapter 15.
Video lessons: watch free lessons on Matching Flaws from teachers on YouTube.
6. Matching Structure and Principles
What it asks: which choice reasons in the same pattern as the original (when the original is valid), or which situation fits a stated principle.
How to work it: compare the form, not the content. For principle questions, check every condition of the rule against the situation; a case that meets only part of the rule does not conform.
Common traps: a choice that matches only the conclusion (Half right) or reverses a conditional (Reversed).
In the book: Chapter 16, Parallel reasoning; Chapter 12, Sufficient assumptions and principles.
Video lessons: watch free lessons on Matching Structure and Principles from teachers on YouTube.
7. Deductions and Inference
What it asks: what follows from the statements given. Some versions ask what must be true, some ask what the statements most strongly support, and some ask what cannot be true.
How to work it: treat the stimulus as facts and look for an answer you can prove, or nearly prove, from them. Combine conditional statements carefully, and watch quantity words such as some, most and all. An answer that goes beyond the facts is wrong even if it sounds reasonable.
Common traps: plausible but unproven claims (Unsupported), overreaching quantifiers (Too strong), and reversed conditionals (Reversed).
In the book: Chapter 10, Inferences and support; Chapter 5, Conditional reasoning; Chapter 4, Precision in language; Chapter 17 for cannot be true and other negative tasks.
Video lessons: watch free lessons on Deductions and Inference from teachers on YouTube.
8. Explain or Resolve
What it asks: which fact would explain a surprising result or make two seemingly conflicting facts both true.
How to work it: state the conflict exactly. The right answer keeps both facts true and shows how they fit together, often by pointing to a difference between the groups, times or measures involved.
Common traps: answers that explain only one side, and answers that deepen the conflict.
In the book: Chapter 14, Evaluate and explain.
Video lessons: watch free lessons on Explain or Resolve from teachers on YouTube.
9. Techniques, Roles, and Principles
What it asks: how the argument works: the method it uses, the role a particular statement plays, or the principle that would justify its reasoning.
How to work it: map the argument first: conclusion, support, counterpoint, background. Then describe the move in general terms (for example, “rejects a proposal by showing it would undermine its own goal”) and find the choice that says the same thing.
Common traps: a description of the wrong statement’s role (Wrong part), and accurate-sounding methods the author never uses (Distortion).
In the book: Chapter 9, Conclusions, roles, and methods; Chapter 12 for principles that justify an argument.
Video lessons: watch free lessons on Techniques, Roles, and Principles from teachers on YouTube.
How often each family appears
The mix varies from test to test. In the official practice test we reviewed in October 2026, the 51 scored Logical Reasoning questions included about 9 Flaws, 9 Assumptions, 8 Strengthen or Weaken, 6 Deductions and Inference, 6 Techniques, Roles, and Principles, 5 Explain or Resolve, 4 Conclusions and Disputes, 2 Matching Flaws and 2 Matching Structure and Principles. The three Think Clearly practice tests follow a similar mix, so your results by family can be compared with the family breakdown on an official score report.
Practice by family
Every Think Clearly practice question names its task and family, and every wrong choice is explained with a trap label such as Too strong, Reversed or Out of scope. The exam simulator reports your accuracy by family and by difficulty after each section, so you can see which chapters to review first. For a one-page view of all nine families, see Chapter 25 of the study guide, A field guide to the Logical Reasoning families. Start with the free diagnostic, or read how the test is structured.
Try one
Here is a Strengthen or Weaken question from the book's free diagnostic. Decide on your answer before you open the explanation.
Sample question · Strengthen · Strengthen or Weaken
Marine ecologist: Over the past fifteen years, the kelp forests along the Varrow coast have shrunk by more than half. During the same period, sea urchins, which graze on kelp, have become far more numerous there, while the sea otters that prey on urchins have declined sharply. I conclude that the loss of otters set off the loss of kelp: with fewer otters to eat them, the urchins multiplied and stripped the kelp beds.
Which one of the following, if true, most strengthens the ecologist's argument?
- A. Many species of fish shelter in the Varrow kelp forests, and several of those species have also declined over the past fifteen years.
- B. Along the Varrow coast, otter numbers began falling several years before urchins multiplied, and the kelp began shrinking only after that.
- C. Along a neighboring coast where otters declined just as sharply, urchin numbers stayed level and the kelp beds remain as extensive as ever.
- D. Over the past fifteen years, water temperatures along the Varrow coast have risen to levels at which kelp grows much more slowly.
- E. Sea urchins can survive for long periods on very little food once the kelp they graze on has been depleted.
Show the answer and why each choice is right or wrong
Answer: B. The ecologist proposes a causal chain: fewer otters, then more urchins, then less kelp. All three changes happened during the same fifteen years, but the argument gives no evidence about their order, and the order matters. If the kelp had begun to shrink first, for instance, the otters might have declined because the kelp was gone, rather than the reverse. Choice B shows the changes occurring in exactly the sequence the hypothesis requires, which makes the proposed chain more likely. Choices C and D point the other way: one shows otter loss without kelp loss, and the other offers a rival cause.
- A: Irrelevant. A decline in fish that shelter in kelp is a further effect of losing kelp and says nothing about what caused the loss.
- B (correct): The changes occurred in the order the hypothesis requires, otters first, then urchins, then kelp, which supports the proposed causal chain.
- C: Weakens instead. A coast where otters declined without urchins multiplying or kelp shrinking suggests that otter loss does not set off kelp loss.
- D: Weakens instead. Warmer water that slows kelp growth is a rival explanation for the shrinking forests that has nothing to do with otters.
- E: Irrelevant. How urchins survive after the kelp is gone does not show what caused the kelp to disappear in the first place.