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Critical Reasoning (CR) is one of the three question types tested in the verbal section of the GMAT. Approximately, one-third of the questions in the test - 13 to 15 of the 41 questions - are from CR. In Critical Reasoning, you will be given a paragraph, called the Argument, with the author of the argument usually drawing a conclusion based on certain facts. Each CR argument is usually followed by one question, and in some rare cases, two.

Critical reasoning questions require that you analyse the author's conclusion and/or the reasoning behind that conclusion. The arguments would be from a variety of topics. However, subject matter familiarity is not a prerequisite to answering these questions.

Broadly, these question types test the following

1. The ability to recognize the structure of an argument and to draw parallels between structurally similar arguments
   
   
2. The ability to evaluate the argument, to recognize factors that would strengthen or weaken the argument
   
   
3. The ability to formulate and evaluate the relative appropriateness and effectiveness of different plans of action
   
   

The questions that test the above abilities may be classified into 10 different types.

1. Identify the Conclusion / Main Point
   
   
2. Identify the Assumption
   
   
3. Weaken the conclusion
   
   
4. Strengthen the conclusion / Explain why
   
   
5. Draw inferences / Must be true
   
   
6. Evaluate the reasoning
   
   
7. Resolve the Paradox
   
   
8. Identify the Reasoning
   
   
9. Mimic the Reasoning
   
   
10. Boldface reasoning
    
    

Here is a sample CR question

Scientists have recently discovered a universal allergy vaccine that would help prevent all kinds of allergic reactions. Allergic reactions - such as watery eyes, a runny nose, and sneezing - are usually caused when the white blood cells release the chemical, histamine. This new vaccine has been created by genetically modifying the allergens and prevents the release of histamines. Thus,the likelihood of suffering from allergic reactions would be greatly reduced by the vaccine.

Q. Which of the following, if true, most effectively questions the effectiveness of the vaccine?

1. This vaccine has been created using very expensive technology and is not likely to be available at an affordable cost.
   
   
2. The release of histamine and the consequent symptoms are the body's mechanism to fight against intruders, including viruses and bacteria.
   
   
3. In some rare cases, allergic reactions are caused even when there is no histamine release.
   
   
4. Although the most predominant, histamine is only one of the many anti-allergen chemicals released by the white blood cells.
   
   
5. Allergic reactions might vary from person to person and it is unlikely that a universal vaccine would work.
   
   

Explanation

The correct answer is (D).

The argument concludes that the vaccine would be effective in reducing allergic symptoms because it blocks histamines. In order to weaken the effectiveness of the vaccine, we need an answer option that establishes that allergic reactions are unlikely to reduce even though the histamines are blocked.

(A) can be eliminated because it discusses the cost effectiveness of the drug and not its effectiveness in preventing allergic reactions.

(E) can be eliminated because the conclusion is not about whether the drug is universal. Moreover, by "universal", the author means that the drug works for every allergy and not whether the drug applies to every person. (E) is therefore, irrelevant

(C) states that allergic reactions without the release of histamines happen only in "rare" cases. However, the author already takes that into account when he states in the conclusion that the likelihood of allergic reactions would be "greatly reduced" and does not state that the reactions would completely stop.

Options (B) and (D) are the closest options. However, option (B) states that the body would become vulnerable to other diseases even though the allergic reactions would stop. The purpose of the vaccine is to reduce the allergic reactions and not to assure optimal health. Other consequences are therefore secondary as this option agrees that the vaccine solves its primary purpose - that of reducing allergic reactions.

Option (D) correctly argues that histamines are only one of the anti-allergens released by the cells and that just blocking histamines might not be sufficient.