When tackling Critical Reasoning questions on the GMAT, many test-takers approach them like puzzles—but famed astronomer Carl Sagan would argue they’re more like scientific claims.
To get them right, you don’t just need verbal skills—you need a baloney detection kit. Sagan’s philosophy of scientific skepticism, distilled in his 1995 book The Demon-Haunted World, offers powerful tools for separating good arguments from bad ones.
This post explores how five key principles from Sagan’s recommended Baloney Detection Kit—and a few classic logical fallacies—can sharpen your CR performance.
GMAT Critical Reasoning questions test your ability to evaluate assumptions, analyze arguments, and spot flaws. These are the same skills Sagan advocates for in everyday thinking. The better you can apply these habits of mind, the easier it is to:
Let’s dive into five of Sagan’s most relevant principles, along with some fallacy detection, and how to apply each on the GMAT.
“Whenever possible there must be independent confirmation of the ‘facts’.”
Don’t take the passage’s claims at face value. Ask yourself: Is this backed by actual evidence, or is it merely asserted? Is the conclusion the only possible interpretation?
Argument: “Our new energy drink improves performance. Five athletes who drank it broke personal records.”
Flawed Reasoning: There is no independent confirmation here. Were there control groups? What else could have led to those results?
Better Answer Choice: One that strengthens the argument by adding independent support—like data from a double-blind trial across many athletes.
In strengthen or weaken questions, ask: Is this claim independently supported? Could the same effect be caused by something else?
“If there’s something to be explained, think of all the different ways in which it could be explained.”
This principle goes hand in hand with eliminating false assumptions. Many wrong answer choices assume that the passage’s explanation is the only explanation. Sagan warns against that.
Argument: “Sales declined because of our new packaging.”
Better Hypothesis: An answer that proposes an alternative cause—perhaps a seasonal dip in demand.
Question Type: Weaken, Evaluate, or Explain a Discrepancy
When you’re evaluating an argument, ask: What are some alternative explanations that could account for the evidence?
“Ask yourself why you like the idea. Compare it fairly with the alternatives.”
Just because an argument sounds “plausible” doesn’t make it logically sound. GMAT CR often includes plausible-sounding wrong answers that reinforce a flawed conclusion. Sagan’s advice? Stay skeptical, and don’t fall in love with the author’s reasoning.
Argument: A WEAKEN question for “Raising the price of gasoline will reduce fuel consumption.”
Tempting Trap: An answer that assumes the author is right, e.g., “Studies show that price increases always reduce use.”
Correct Answer: One that either questions the assumption (e.g. “People may switch to fuel-efficient cars but drive more”) or offers a competing conclusion (e.g. seasonal variances in fuel use).
If an answer choice simply rewords or affirms the passage’s logic, be suspicious. The best answers often test the limits of the argument’s assumptions.
“Arguments must be valid at every step. Not just the conclusion, but each premise and the connection between them.”
Think of an argument as a chain. If one link breaks—one flawed assumption, one weak premise—the whole thing collapses. Your job is to pressure-test each link.
Argument: “Crime dropped after the new policy, so the policy must be effective.”
Answer trap: “The policy was widely praised by police officers” — this is Out of Scope because it is irrelevant to the causal chain.
Best answers: These will challenge or reinforce the causal link, not just provide surface-level details.
In assumption questions, always identify the weak link. Ask: Does this conclusion truly follow from the premises? Then look for answers that bridge the gap or expose the gap.
“Can the hypothesis be disproven? If not, it’s not a scientific claim.”
GMAT arguments often rely on vague or unfalsifiable premises. If a claim can’t be tested, it can’t be logically verified or challenged—which makes it useless in argumentation.
Argument: “Employee morale is higher now, so productivity will rise soon.”
What’s missing? No way to test what “morale” means or how it translates to future outcomes. Essentially, we have no idea how productivity would be linked to employee morale so we have no grounds to make such a claim.
Good answers: Probe whether the claim is measurable. E.g., “Employee surveys show morale changes don’t predict output.” Try to find an answer that provides a measurable link between morale and employee productivity.
Trap answers: Rely on emotions, beliefs, or undefined ideas.
Ask: Can I imagine a real-world test that could disprove this? If not, the argument is weak, and good answer choices will challenge its testability.
Now let’s add some fallacy detection. Here are a few of Sagan’s logical fallacies you’ll see disguised as tempting answer choices.
“This expert is wrong because he’s a lobbyist.”
On the GMAT, attacking the source of an argument rather than its logic is irrelevant. Note: this is a fairly rare case and will likely be a situation where we need to identify the the nature of how one person responds to another’s argument.
NB: these are also possible as Two-Part Analysis questions in Data Insights.
his is more common in questions that have competing debaters.
“We don’t have proof the product is unsafe, so it must be safe.”
This fallacy assumes that lack of evidence is itself evidence.
“Either we increase spending or the system will collapse.”
The GMAT loves to present only two choices when others exist. It’s not necessarily one or the other. It could be both and.
Carl Sagan wasn’t advocating negativity. His brand of skepticism was curious, humble, and clear-eyed.
That’s the mindset you need on GMAT CR. Don’t just doubt for the sake of doubting—evaluate carefully, and stay alert to the baloney.
The GMAT wants to know: Can you think critically? Can you follow an argument—and challenge it when it gets lazy? With the tools Sagan gives you, the answer can be yes.
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