Solving Short Logic Passages on the GRE
Mixed in with your sentence completions and short and long reading passages on the GRE will be a few “logic” passages. They ask questions about the logic of the passage, usually an argument or analysis, and focus on the passages’ implications, assumptions, and conclusions. These logic passages can be one of the trickier parts of the GRE. In this guide we will look at what is contained in a short logic passage, how to solve them, and try a few sample passages (don’t worry, we’ll also give you the answers!).
Logic Review
An argument or analysis is based on three components:
- the data (or facts)
- the assumptions
- the conclusions or implications
The data is the starting point of an argument or analysis and the conclusion is the end. You link data to a conclusion or to implications by making assumptions. You can either make those assumptions explicitly or implicitly.
Your job with any logic passage is to identify the “facts” and the conclusion. Usually, that’s fairly easy. The more difficult part is to identify the assumptions. Remember: the assumption links the facts to the conclusion. So when you’re trying to find the assumptions, just ask yourself “How do I get from the facts to the conclusion?”
Logic questions won’t always ask you to find the assumptions, but finding the assumptions will be helpful in many regards. First, if you want to weaken or strengthen an argument, you’re usually weakening or strengthening the assumptions. Second, if you’re looking for “implications,” then often you’re trying to find the assumptions.
But don’t overthink “implication” questions. Usually, an “implication” is just another way to state the conclusion. And keep in mind that no matter what the question is asking, the information is always in the passage. Unless the question explicitly asks you to add new information, you must work only with the information in the passage.
Sample Logic Passage 1
The discovery of distinctively shaped ceramic pots at various prehistoric sites scattered over a large geographic region has led archaeologists to question how the pots were spread. Some believe the pot makers migrated to the various sites, carrying the pots along with them; others believe that the pots were spread by trade, while their makers remained in one place. Now, analysis of the bones of prehistoric human skeletons has led some scientists to believe that high concentrations of a certain metallic element in the human skeleton is indicative of migration to a new location after childhood. Many of the bones found near the pots at a few sites showed high levels of this metallic element. Therefore some scientists conclude that the pots were spread by migration.
Select the best answer choice:
- Which of the following could be inferred from the passage?
a. Archaeologists now suspect that the pots in question were spread by trade.
b. Archaeologists assume that the distinctive shape of the ceramic pots is indicative of their common cultural origin.
c. The sites in question were probably centers of trade.
d. Archaeologists believe that the pots were manufactured in order to store supplies during migration.
e. The high levels of the metallic element found in prehistoric skeletons of people who migrated are not to be found in the bones of modern people.
- Which of the following facts would most directly weaken the conclusion that the pots were spread by migration?
a. The style of the pots at the various sites was found to be uniform.
b. The style of the pots at the various sites was found to differ subtly from site to site.
c. Analysis of the pots revealed that the clay from which they were made came from a common source hundreds of miles away from the sites in which they were found.
d. Comparably high levels of the same metallic element found in the prehistoric skeletons were also found in modern people who had lived their entire lives in the same regions as the sites where the pots were found.
e. Ceramic pots of the same style were found at a new site that predated the sites analyzed by several thousands years.
Sample Logic Passage 2
How did the earth acquire its oceans? According to one theory, water in the earth’s oceans originated from comets. As the earth was being formed out of the collision of space rocks, the energy from those collisions and from the increasing gravitation of the planet made the entire planet molten, including the surface. Any water on the planet’s surface would have evaporated and been released into space. As the planet approached its current size, its gravitation became strong enough to hold an atmosphere of gases and water vapor around the planet. Because comets are mostly ice made up of frozen water and gases, a comet striking Earth then would have vaporized. The water vapor that resulted would have been retained in the atmosphere, eventually falling as rain on the now cooled and solidified surface of Earth.
Select the best answer choice:
- Which of the following would most directly undermine the theory discussed above?
a. Of all comet impacts with the earth, the vast majority occurred while the planet still had a molten surface and no atmosphere, while only a small number of relatively tiny comets have struck since the earth acquired an atmosphere.
b. As the planet approached its current size, volcanic activity increased, releasing steam and other gases into the atmosphere.
c. The atmospheric pressure increased as the earth cooled, slowing the rate of evaporation of water.
d. The earth’s moon has no water, although it too has been struck by comets.
e. An analysis of a sample of water taken from a comet showed that it had a similar composition to the water found in the earth’s oceans.
Consider each answer choice separately and select all that apply.
- Which of the following statements is supported by the passage?
a. Earth’s early atmosphere was probably formed largely by comets.
b. Earth’s gravitation was weaker when it was first forming.
c. The space rocks which formed the body of Earth probably held very little water.
d. The comets which impacted with Earth were probably very large.
e. The atmosphere of early Earth was made up of gases released by volcanic activity.
Sample Logic Passage 3
The mental–health movement in the United States began when Dorothea Dix successfully campaigned for the national establishment of asylums where the mentally ill could be cared for. By the early 1900s, however, asylums were underfunded by the government, and became places where overcrowding, neglect, the use of force, and abuse were common. After World War II, however, new medications were discovered for some major mental illnesses previously thought untreatable (penicillin for syphilis of the brain and insulin treatment for depression and schizophrenia); newspaper exposés and books focused public attention on the plight of the mentally ill; and Dr. David Vai’s Humane Practices Program was founded, becoming a model program for future efforts to reform other asylums. But substantial change took place only in the 1960s, when the civil–rights movement led lawyers to investigate America’s disproportionately high population of black prisoners in jails and asylums. Patients’ rights groups, formed by these lawyers, successfully lobbied for reform in the state legislatures.
Select the best answer choice:
- It can be inferred from the passage that which of the following factors contributed to post–World War II reform of state mental institutions?
a. An increase of funding provided by state legislatures to rehabilitate asylums.
b. The invention of drugs to sedate and otherwise render passive mental patients.
c. The discovery of effective treatments for illnesses that were previously considered untreatable.
d. Realization that some criminal behavior is due to mental illness.
e. Advances in penology that discredited the effectiveness of incarceration.
- The passage provides information that would help answer all of the following questions EXCEPT:
a. Who are some of the influential figures in the history of the public health movement in the United States?
b. What were some of the mental illnesses that went untreated before the 1950s?
c. What were some of the more influential legal cases that shaped the legislation of patients’ rights?
d. How did the civil–rights movement help to bring about the legislation of patients’ rights?
Answers and Explanations
Here are the answers and explanations to the above passages.
Passage 1
- b. The key is that archeologists wonder how the “pots were spread.” They present two alternative theories: either, that the “pot makers” migrated, or that they sold the pots, which were then carried to distant locations. Both theories assume that the pots were made by “pot makers” of a specific culture, rather than theorizing that this unique shape could have been common to many different settled peoples over a wide geographic range.
- d. If high levels of this metallic element are endemic to the regions where the bones were found, then we cannot assume that these high levels are indicative of migration.
Passage 2
For “select the best answer choice.”
- a. If the vast majority of comet impacts occurred when the earth had no atmosphere, this means they occurred when the earth was not large enough to retain an atmosphere. Consequently the water contained in the comets would have escaped into space. It seems likely that a “small number of tiny comets” whose water would have been retained in the atmosphere would not account solely for Earth’s oceans.
For “select all that apply.”
- b. The clue is that “as the planet approached its current size, its gravitation became strong enough … to hold an atmosphere.” This means that while it was smaller, the earth had a weaker atmosphere than at present.
Passage 3
- c. The clue is that the word “however” contrasts pre-World War I conditions with post-World War II conditions, “when new medications were discovered for some major mental illnesses.” This suggests that the medications helped lead to changes in care of the mentally ill.
- c. There are no examples given of specific legal cases that were fought on behalf of the mentally ill.
Now that you know how to solve these logic passages, you’re that much closer to acing the GRE! Good luck!
From The Complete Idiot’s Guide to Acing the GRE by Henry George Stratakis–Allen
