In the last few chapters you’ve played an observational role notating the structure of arguments, flaws in arguments, and finding similar flaws. In this chapter we’re doing a more complex task: we’re fixing broken arguments (or weakening them). This is the final and hardest chapter in the Logical Reasoning course. The questions in this chapter will typically be in the second half of the sections, where the more challenging questions typically dwell.

CHALLENGE: Weaken Key Assumptions

Weaken questions ask you to find statements decrease (weaken) the strength of an argument. Since the premises are taken to be true, the way to decrease the strength of an argument is to attack it’s assumptions that the argument relies upon. A weaken correct choice doesn’t need to demolish the argument completely; it’ll just make it significantly weaker.

Here are some examples of Weaken Argument question stems:

  • Which of the following, if true, most seriously weakens the conclusion drawn above?
  • Which of the following, if true, would provide the strongest evidence against the above?
  • Which of the following, if true, casts the most serious doubt on the conclusion drawn above?

Next LSAT: January 26

Tips for Weaken Questions:

  1. Try to find one necessary assumption in the passage. This is what the right weaken answer will often target.
  2. Causal fallacies (will be reviewed below) are very common on these questions. These questions typically try to say that A caused B. You are either going to weaken or strengthen that causal argument.
  3. When you see a Weaken question that compares two things or tries to show them as similar, look for an underlying factor that makes such a comparison problematic.
  4. There will likely be two or more choices that weaken the argument. In this case, re-read the passage carefully and see which one is most directly relevant to the premises, the conclusion, and the assumptions. The final answer that remains is the correct answer.
  5. Common trap answer choices include:
    • A statement that strengthens (and doesn’t weaken) the assumptions and the overall argument — a trick. This is the opposite of what you want.
    • A statement with information not relevant to the argument.
    • A statement that requires additional facts to have value.

Use strong language to strengthen or weaken. On most other Verbal questions, you can eliminate potential answers that use strong language. The exception are the Strengthen/Weaken questions. On these questions, sweeping words are more effective:

  • only
  • the most
  • extremely
  • all

The reason? Extreme answers will have a more powerful weakening/strengthening effect on assumptions

Example #1

In many pre-schools, children commonly tend to get colds before their resistance develops, and the colds become much less frequent. It is clear that a child requires several colds before white blood cell concentrations rise high enough to effectively deal with colds.

Which of the following, if true, most seriously weakens this theory?

  1. Children commonly spread viruses and bacteria in a small, closed environment.
  2. The use of Vitamin C increases resistance to the common cold and decreases its frequency.
  3. Parents stock up on cold medicine that alleviates the symptoms of a cold after a child gets sick.
  4. There are many strains of the cold virus, and children develop resistance to individual strains.
  5. White blood cells fight infection, and their production levels are stimulated by high infection levels.

Example #1 Explanation

The question is stating that the body’s immune system requires numerous infections to be properly stimulated. It is a causal argument that tries to explain an observation.

Premise #1: Children tend to get fewer colds as they progress through pre-school.
Premise #2: (unstated assumption)
Conclusion: It takes several colds to activate a child’s immune system.
Analysis: This is After This, Therefore, Because of This fallacy. It observes that as children go through pre-school the number of colds goes downs. From this, the creative author develops the theory that a child’s immune system requires them to get several colds before it is fully activated.

The best way to weaken a causal argument is to suggest an alternative causal factor.

Reviewing Answer Choices

Children commonly spread viruses and bacteria in a small, closed environment. Not Relevant

The use of Vitamin C increases resistance to the common cold and decreases its frequency. Not Relevant

Parents stock up on cold medicine that alleviates the symptoms of a cold after a child gets sick. This choice presents another possible reason to undermine the argument, but the medicine deals with symptoms, not the cold per se. So it is not reducing an instance of a cold but simply decreasing its symptoms (no more runny noses!).

There are many strains of the cold virus and children develop resistance to individual strains. This choice suggests an alternative explanation for the apparent improvement in a child’s ability to fight colds: the child simply becomes immune to individual viruses. So, the theory that a child’s immune system needs high white blood cell concentrations isn’t the case; it is an issue of exposure to certain strains. By suggesting a different causal process to explain the reduction in colds, it weakens the argument.

White blood cells fight infection, and their production levels are stimulated by high infection levels. This choice supports this statement, but the question asks for what weakens it.

Trick opposites are sometimes used as junk answer choices on Strengthen/Weaken questions. If the stem asks for what weakens the passage, you’ll find a perfect answer choice for what strengthens it, and vice versa. Choice (E) in the above question about colds is an example of a trick opposite.

Weaken Arguments

Next LSAT: January 26