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Correct By Choice, Not By Chance: Logical Reasoning in CARS

  • by Sam
  • Nov 21, 2016
  • MCAT Blog, MCAT Prep

The Critical Analysis and Reasoning Skills (CARS) section of the MCAT is often the most intimidating section for students. Unlike the sciences, there is no shelter of content to feel safe with, no set of content you can simply master in order to improve. However, there is a set of predictable, learnable skills which will enable you to score highly on the CARS section. Practice with these skills will ensure you can answer even tough skill 2 and skill 3 questions which require you to read between the lines of the passage. These skills are two types of logical reasoning – Deductive and Inductive reasoning.

Deductive Reasoning

Deductive reasoning is where one begins with an accepted principle and seeks to prove another statement based on previously “known” information.

For example, if a physician walks into the exam room with the premise that there has been a recent spread of MRSA, the new patient is likely another infection so she gathers information — blood tests, cultures, a physical exam — and narrows the scope of that available information until MRSA (her principle) is the only logical conclusion remaining.

This is the kind of logic that, many physicians may use: they have a diagnosis in mind based on previously available information that is not necessarily related to the new patient, and then they seek out evidence to prove that diagnosis. The MCAT will ask you to do this in questions that require you to find evidence that supports or weakens a passage argument, or when they ask you to identify assumptions in passage arguments.

Inductive Reasoning

Inductive reasoning, conversely, allows physicians to extrapolate from the information gleaned from patient interaction in order to arrive at a diagnosis about a disease that has not been observed.

This type of reasoning was made famous by Sherlock Holmes and his medical counterpart, Dr. Gregory House. Here, the irascible Dr. House will enter the exam room a blank slate; he has no pre-supposed ideas about a diagnosis. Maybe the patient has lupus, maybe they have rheumatism, and maybe it is some environmental toxin. House does not know. So his team investigates and performs tests. There’s a positive antinuclear antibody test result, no one else in her home or work is sick so she could not been exposed to a toxin. There’s the inflammation, but that could be rheumatoid arthritis. Does she have any CNS issues? Any histone antibodies? House continues to gather information until he arrives at a conclusion (which was often incorrect for the first few tries). More patient information will come until House is quite sure he’s arrived at the right diagnosis.

This is a much more common method of medical practice and the test makers will also test your ability to do this kind of reasoning in questions that require you to reach conclusions based on presented evidence, or to guess at the author’s opinions or intentions given what they have written in the text.

In Practice

In all MCAT questions, we can rest assured that there is only 1 correct answer, and the other 3 are literally written to be wrong.

Most MCAT arguments will contain 2 parts that are provided and 2 that are asked for. Evidence and conclusions (premises) are in the text, while the questions will ask you to identify assumptions and inferences implied by the passage. A good rule of thumb to use is that valid assumptions are those that are necessary to the opinions (i.e. premises) in the passage. On the MCAT, correct inferences are logical conclusions which must be true if the passage arguments are true.

We do not need to go hunting for information; it will always be provided to us in the text, or the questions themselves. You too can master the art of MCAT logic.

Try to identify the logic in the three examples below:

  1. Most government officials just want to raise my taxes. At least most of the politicians I have voted for.
  2. Amy needs psychiatric treatment. After all, she is homeless.
  3. The news about Nia is that she’s recovering from surgery and has decided to attend physical therapy.

Check your answers below, and be sure to jump into CARS practice right away, as there is no prerequisite knowledge.

Dr. Anthony LaFond, Former Director of MCAT Content


Answer Key:

  1. Inductive logic – note keyword of “most” and projection of personal experiences.
  2. Deductive logic – note that the premise “All homeless are mentally unstable” is implied.
  3. This is not an MCAT argument – there is no conclusion

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