Biologists with a predilection for theory have tried—and largely failed—to define what it is that makes something a living thing....

GMAT Critical Reasoning : (CR) Questions

Source: Official Guide

Critical Reasoning

Logically Completes

MEDIUM

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Notes

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Biologists with a predilection for theory have tried—and largely failed—to define what it is that makes something a living thing. Organisms take in energy-providing materials and excrete waste products, but so do automobiles. Living things replicate and take part in evolution, but so do some computer programs. We must be open to the possibility that there are living things on other planets. Therefore, we will not be successful in defining what it is that makes something a living thing merely by examining living things on Earth—the only ones we know. Trying to do so is analogous to trying to specify ______.

Which of the following most logically completes the passage?

the laws of physics by using pure mathematics

what a fish is by listing its chemical components

what an animal is by examining a plant

what a machine is by examining a sketch of it

what a mammal is by examining a zebra

Solution

Passage Analysis:

Text from Passage	Analysis
Biologists with a predilection for theory have tried—and largely failed—to define what it is that makes something a living thing.	What it says: Scientists who love theory have mostly failed to define what makes something alive What it does: Sets up the problem - there's a challenge in defining life that hasn't been solved yet What it is: Author's opening claim about scientific failure
Organisms take in energy-providing materials and excrete waste products, but so do automobiles.	What it says: Living things eat and produce waste, but cars do this too (fuel in, exhaust out) What it does: Gives first example of why defining life is tricky - shows a supposed life characteristic that non-living things also have What it is: Supporting evidence for the difficulty claim Visualization: Living organism: Food → Energy → Waste vs. Car: Gas → Energy → Exhaust
Living things replicate and take part in evolution, but so do some computer programs.	What it says: Living things reproduce and evolve, but some computer programs do this too What it does: Provides second example that reinforces the same point - another "life" trait that non-living things can have What it is: Additional supporting evidence
We must be open to the possibility that there are living things on other planets.	What it says: We should consider that life might exist elsewhere in the universe What it does: Introduces a new angle - expands the scope beyond just Earth life What it is: Author's premise about expanding our perspective
Therefore, we will not be successful in defining what it is that makes something a living thing merely by examining living things on Earth—the only ones we know.	What it says: We can't successfully define life by only looking at Earth life since that's all we currently know What it does: Draws a conclusion from the previous points - combines the definitional problems with the possibility of alien life What it is: Author's main conclusion
Trying to do so is analogous to trying to specify _____.	What it says: The passage sets up an analogy comparing this flawed approach to some other similarly flawed approach What it does: Prepares to reinforce the conclusion through comparison What it is: Setup for analogy completion

Argument Flow:

The argument starts by identifying a scientific problem (failure to define life), then shows why it's difficult with concrete examples (cars and computer programs sharing life-like traits). It then expands the scope by considering alien life, and concludes that studying only Earth life is insufficient for creating a universal definition. Finally, it sets up an analogy to reinforce this point.

Main Conclusion:

We cannot successfully define what makes something a living thing by examining only Earth life - the approach is fundamentally flawed because our sample is too limited.

Logical Structure:

The evidence (examples of non-living things with life-like traits + possibility of alien life) supports the conclusion that Earth-only examination is insufficient. The logic is: If life characteristics overlap with non-life AND life might exist elsewhere with different characteristics, THEN studying only Earth life gives us an incomplete picture for making a universal definition.

Prethinking:

Question type:

Logically Completes - We need to find an analogy that parallels the flawed approach of trying to define life by only examining Earth-based examples when broader possibilities exist

Precision of Claims

The key claim is that defining life solely from Earth examples is flawed because: 1) Current Earth-based criteria overlap with non-living things, and 2) We must consider possible alien life forms that might be different

Strategy

Look for analogies where someone tries to define or specify something based on a limited sample when they know (or should know) that there are broader possibilities they haven't examined. The analogy should capture both the limitation of the sample and the awareness that there are unknown examples that could change the definition.

Answer Choices Explained

the laws of physics by using pure mathematics

This doesn't match the argument's logic. The issue isn't about using the wrong method (math vs. observation), but about having too limited a sample. Physics laws are actually universal principles that can be derived mathematically, so this approach isn't fundamentally flawed like the life-definition approach.

what a fish is by listing its chemical components

This analogy focuses on using the wrong approach (chemical components vs. biological characteristics), not on having a limited sample size. The argument's flaw is about examining too narrow a range of examples, not about using the wrong analytical method.

what an animal is by examining a plant

This analogy suggests examining something completely different from the target category. But the argument isn't about studying the wrong type of thing - it's about studying too limited a sample of the right type of thing (only Earth life, not all possible life).

what a machine is by examining a sketch of it

This analogy is about using an incomplete or indirect representation rather than studying a limited sample of actual examples. The argument's flaw isn't about studying representations vs. real things, but about studying too narrow a range of real examples.

what a mammal is by examining a zebra

This perfectly captures the argument's logic. Just as trying to define all mammals by studying only zebras would miss the diversity of mammals (whales, bats, humans have very different characteristics), trying to define all life by studying only Earth life misses potential diversity in alien life forms. Both involve using too limited a sample from within the correct category to make a universal definition.

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