GMAT Weaken CR: Correct Weakener Standard | OG | Salmonella

This post uses the Official GMAT question that begins "A lethal strain of Salmonella recently showed up in a European country" to explain the standard every correct Weaken answer must meet.

If you are just starting with Weaken questions, or have been practicing them for a while without consistent results, the simplest way to reach the correct answer is to know exactly what a correct weakener looks like. When that picture is clear, you stop judging choices by how strongly they seem to disagree with the argument and start checking each one against a fixed standard.

The Standard Every Correct Weakener Meets

Here is that standard. A correct weakener brings in a new piece of information that reduces your belief in the conclusion, without challenging any premise.

Each part of that definition matters, so it is worth taking them one at a time.

First, it brings in new information. The correct choice adds something the argument did not already tell you. A choice that restates or explains a premise adds nothing new, so it cannot change how you see the conclusion.

Second, it reduces your belief in the conclusion. It does not have to prove the conclusion false. It only has to make you trust the conclusion less than you did before you read it. If you reject a choice because it leaves room for the conclusion to still be true, you are holding a weakener to a standard it never had to meet.

Third, it does not challenge any premise. In Critical Reasoning, premises are accepted as true. This holds for every question type, not just Weaken: no correct answer goes against a premise. So the job of a weakener is never to show that a stated fact is wrong. Its job is to show that, even with every fact standing, the conclusion no longer follows as well as it seemed to.

The Question Setup

Let's see how this works in a question.

In this question, a microbiologist responds to investigators. The investigators blamed the severity of a Salmonella outbreak in a European country on the overuse of antibiotics, because the bacteria tested were drug resistant. The microbiologist disagrees and concludes that this is unlikely. The reason: patients in that country cannot get antibiotics without a prescription, and the country's doctors prescribe antibiotics less readily than doctors in any other European country.

Before looking at the choices, apply the standard to this specific conclusion. The correct answer must bring in new information that makes it more believable that antibiotic overuse could have contributed to the severity of the outbreak, while leaving both premises intact. You have to accept that prescriptions are required, and you have to accept that doctors prescribe sparingly.

That last requirement already rules out a whole category of choices. A choice claiming that doctors in this country actually prescribe antibiotics freely, or that patients easily get them without a prescription, might feel like a strong attack on the argument. But it contradicts a premise, so it cannot be the correct answer.

The Correct Answer, Checked Against the Standard

Now look at the correct choice: people in the country often eat foods produced from animals that are given antibiotic laden feed.

Check it against the three parts of the standard. Is it new information? Yes. The passage says nothing about food or livestock. Does it challenge a premise? No. Prescriptions are still required, and doctors still prescribe sparingly. Does it reduce your belief in the conclusion? Yes. The microbiologist's reasoning treats prescriptions as the way people get antibiotics. This choice gives another way: antibiotics given to animals can reach people through the food they eat. If people are consuming antibiotics this way, then overuse of antibiotics is possible despite strict prescribing, and the conclusion that overuse is unlikely becomes harder to trust.

Notice what the choice did not do. It did not prove that antibiotic overuse caused the severity. It did not say how much antibiotic reaches people through food. It only gave you a reason to believe the conclusion less, and that is all a weakener needs to do.

The Habit This Builds

In this question, the weakener works by pointing to a possibility the argument did not account for. That is how this particular choice works, not a rule for every Weaken question. Different arguments leave different gaps, and correct weakeners work on them in different ways. What stays the same in every Weaken question is the standard itself: new information, less belief in the conclusion, no premise challenged.

That is why it is worth defining what the correct answer must convey before you read the choices. When you know the standard and have applied it to the exact conclusion in front of you, you are not searching for the choice that sounds most opposed to the argument. You are checking each choice against a clear definition, and the correct one is much harder to miss.

Part of the Weaken Beginner Series

This question is part of the Weaken Beginner Series, in which easy Official GMAT questions are used not to test what you know, but to reveal how you think. Each question targets a specific reasoning habit, one that shows up in a simple form on easy questions and a complex one on hard questions. If you are getting started with Weaken questions or if Weaken questions feel inconsistent for you, this series is built to show you exactly where the process is breaking down.

Solve the question on your own first. The reasoning you apply matters more than the answer you reach.

Once you know the standard, the next step is to see where your own process departs from it. The free CR diagnostic at gmatquizmaster.com gives you personalized feedback on your attempt, so you can see which step needs work.

What Every Correct Weakener Must Do: The Standard That Simplifies Weaken Questions