LSAT-Section-1-Logical-Reasoning – Section One : Logical Reasoning

Reference / correct answer:

Argument construction

A test that examines people on their memory capacity for spatial layouts has placed Jason in the top 1 percentile of all test-takers. We can conclude from this that his memory capacity for things that do not involve spatial layouts will be below average.

The structure of the argument is:

Premise: Jason is in the top 1 percentile of all people in his memory capacity for spatial layouts. This means, his 'memory capacity for spatial layouts' (called Ms henceforth for easier reference) is better than 99% of all test-takers. In other words, it is outstanding!

Conclusion: We can conclude from this that his memory capacity for things that do not involve spatial layouts (called MO – 'o' for other things - henceforth for easier reference) will be below average. Looking at this argument, we see a gap between the premise and conclusion – being outstanding in MS does not necessarily guarantee that one's MO will be below average. This is the loophole that the correct answer choice will have to plug. The correct answer choice will be one which, when added to the argument's premise, would produce a conclusive argument, that is, an argument with no gaps in its support for the conclusion.

Let us analyze the options one by one.

Answer choices explanation

[Jason tried hard to remember spatial layouts.] This option is incorrect. When we take this option statement as a premise and combine it with the premise of the argument, does the conclusion logically follow? No. This option statement only provides a plausible reason for why Jason's MS is outstanding. It does not offer any support for the conclusion, which is about his MO.

[Jason has a greater proclivity to remember spatial layouts than most people.] This option is incorrect. The reasons are similar to the ones discussed in the Option above.

[It is possible for Jason to improve, through practice and effort, his memory capacity for things that do not involve spatial layouts.] This option is incorrect. The premise in the argument is that Jason's MS is outstanding. The premise offered by this option statement is that it is possible for Jason (through practice and effort) to improve his MO. When these two premises are combined, the conclusion that Jason's MO is below-average does not logically follow. In fact, one wonders how, when it is possible to improve one's MO, can such a definite declaration as the argument's conclusion be made.

[The total memory capacity of the human brain is fixed and equal for all people.] This option is correct. According to this option statement, the total memory capacity, M, is equal for all people. Also, M is a fixed number. It cannot be increased or decreased. Now, If Jason has higher MS than most people, then it does follow that his MO is lower than most people. Therefore, when this option statement is combined with the argument's premise, there is no gap left in the argument and the conclusion follows logically.

[Some people have a greater memory capacity than others.] This option is incorrect. If some people have a greater (total) memory capacity than others, then it could be possible that Jason has both an outstanding MS and an outstanding MO, therefore, ending up with an outstanding total memory capacity M as compared to most people. Therefore, when this option statement is combined with the premise, the conclusion does not logically follow.

Reference / correct answer:

Argument construction This year:

"the cotton crop in Alabama has been attacked by a new, hardy variety of bollworm that is resistant to all known pesticides." This is context-setting information. "Due to this, the cotton production of the state has declined by 40 percent this year." This is Premise 1.

Premise 2: "this bollworm variety reproduces rapidly."

Premise 2 leads to a Subsidiary Conclusion: "[this bollworm variety] is likely to spread through all cotton-producing states of the United States by the next year."

Premise 1 and the Subsidiary Conclusion are then combined to reach the Main Conclusion: "we can expect a decline of at least 40 percent in the amount of cotton produced in the country next year."

There are a few gaps in the way this argument has been made:

It has been assumed that what has happened in Alabama will happen in all cotton-producing states of the country. Premise 1 mentioned a 40 percent decline in cotton production in only Alabama. However, using this premise, a conclusion was drawn that there will be a 40 percent decline across all cotton-producing states of the country next year. Clearly, this generalization is unfounded and if attacked or proved wrong will significantly weaken the conclusion drawn in the argument.

Another type of generalization that has been made in the argument is time-based. Premise 1 presents facts that happened this year. And using this premise, a conclusion is drawn about what will happen next year. Such extrapolation of this year's information to make a prediction for the next year is a logical leap and the argument will be weakened if a reason is provided for why this year ought not to be used as the basis of future predictions. For example, it could be that the weather in Alabama this year was unusually hot but it is expected to be normal again the next year. In this case, the bollworm variety, which thrives in unusually hot weather, may lie dormant or even perish next year because the weather next year may be unfavorable to it.

Premise 2 offers only a very weak support to the subsidiary conclusion. Premise 2 mentions that this bollworm variety reproduces rapidly. For example, say, its population takes only 24 hours to double. This only suggests that its population in Alabama where this bollworm variety is found now will increase significantly by next year. But will it necessarily spread to other cotton-producing states? Does this bollworm variety have the physical capacity to travel long distances or some other means to travel or reach new places? If evidence is presented to suggest that the answer to these questions is No, then the Subsidiary Conclusion is proved wrong, and consequently the Main Conclusion gets significantly weakened.

Let us analyze the options one by one.

Answer choices explanation

[Many other crops in Alabama too have been attacked by...] This option is incorrect. The conclusion drawn concerns only the cotton crop (across all cotton-producing states of the country, next year). The impact of this bollworm on other crops of Alabama does not impact the argument.

[The natural predators of this bollworm variety are not able to survive in Alabama…] This option is correct. This statement suggests one reason why it would be wrong to use what happened in Alabama to make a prediction for what will happen in other cotton-producing states. A point of difference between Alabama and these other states is that Alabama does not have the natural predators of this bollworm variety, whereas the other states have these predators in large numbers. This suggests that in the other states, the population of this bollworm variety will be controlled (by natural predators present in cotton forms) and therefore, it will not be able to wreak as much havoc as it did in Alabama this year. Therefore, when this option statement is used in conjunction with Premise 1, the main conclusion appears much weaker.

[Ninety-five percent of all cotton produced in the United States is of the Upland variety…] This option is incorrect. Had the variety of cotton grown in Alabama been different from that grown in the other cotton-producing states of the United States, the conclusion would have been weakened. For example, one could have supposed that perhaps this bollworm variety had a deleterious impact on only the Alabama variety of cotton, and that its impact on the other varieties of cotton would be mellower or negligible. However, this option statement says that Alabama also grows the same variety of cotton that makes for 95 percent of all cotton grown in the United States. This option statement, therefore, establishes a point of similarity between Alabama and the other cotton-producing states and, thus, supports the use of Alabama-based Premise 1 to make a general conclusion for all cotton-producing states.

[The domestic prices of cotton are not likely to increase…] This option is incorrect. The argument makes no prediction or claim regarding the domestic prices of cotton next year. Therefore, this option statement is out of the argument's scope.

[Agricultural scientists in the United States are making a massive effort...] This option is incorrect. On the face of it, this option seems to suggest that the efforts of the agricultural scientists might prevent the predicted decline of cotton production next year by creating cotton plants that are immune to this bollworm variety. However, on closer inspection of the statement, we start to notice flaws in it. For example, the word "soon" is qualitative. What time frame does it convey? One month, or six months, or one year, or five years? This is not clear. On the other hand, the conclusion concerns itself very clearly with the next one year. Further, even if such a variety of cotton gets developed before next year, will it immediately get adopted on a large scale, across all cotton-producing states of the United States? This seems unlikely. Therefore, it does not seem plausible that these efforts of agricultural scientists will undermine the conclusion drawn by the argument.

Reference / correct answer:

Argument construction

Premise 1: A study of young and middle-aged men in the United States has found that the men whose diet was high in saturated fat (SF) also had a high amount of blood cholesterol (BC).

So, this premise can be simplified as: High SF is correlated with high BC in young and middle-aged American males.

Premise 2: In another experiment, when the blood cholesterol level (BC) of laboratory rabbits was raised by feeding them on cholesterol, fat deposits (FD) were found in their blood vessels.

This premise can be simplified as: In lab rabbits, when BC became high, FD formed.

Premise 3: Similar fat deposits (FD) are found in human patients of heart disease (HD).

So, per this premise, FD is correlated with HD in humans.

By combining these three premises, the following conclusion is drawn:

Conclusion: To reduce the occurrence of heart disease, people should reduce their dietary consumption of saturated fat.

In simpler form: To reduce HD, people should reduce SF.

The structure of this argument can be visually depicted as under:

There are a few things to note about the way this argument is drawn:

The argument's conclusion draws broad generalizations whereas the premises are not similarly general in their scope:

1. Premise 1 mentions a finding about one demographic - young and middle -aged American men – while the conclusion drawn is a generalization that seems to apply to all "people," irrespective of age, gender or nationality.

2. Premise 2 mentions a finding about laboratory rabbits while the conclusion drawn is about humans. The argument confounds correlation with causation.

This is proved by the conclusion that reducing SF will cause reduced occurrence of heart disease. However, the premises do not offer grounds for such causality:

1. Premise 1 only states that in one particular group, high SF is correlated with high BC. We cannot infer from this whether it is high SF that caused high BC, or whether high BC caused high SF (for example, by inducing cravings for food that is high SF), or whether some other third factor was the cause of both high SF and high BC (for example, if the individuals of this particular group have a genetic predisposition towards higher BC than other ethnic and/or age groups and also have a diet that is high in SC).

2. In Premise 2, since FD follows an increase in BC, the said increase in BC does seem to cause the FD; however, this causal link is still an assumption and is not explicitly stated by the argument. Alternate explanations might be possible. For example, since these rabbits were fed exclusively on cholesterol, perhaps they developed deficiency of some vital nutrient X (which they usually got from their normal diet) and it was the lack of this nutrient X that caused the formation of FD. With such an explanation, one can see that if the rabbits had continued to consume as much cholesterol as they did in this study but along with the required amounts of X, they would not have formed FD.

3. In Premise 3, FD is found in human patients of HD. This is not enough to conclusively establish that FD causes HD in humans. For example, when the virus of common cold enters the human body, the body activates its immune system and produces antibodies to neutralize that virus. There is a brief period when, if a blood sample is taken from the body, both the virus and the antibodies will be found in it. From this coexistence, drawing a conclusion that the antibodies produced/caused the virus would be wrong. Correlation does not always imply causality, and even when it does, the direction of that causality is not always clear (if A and B coexist, then does A cause B or does B cause A?).

Not only does the argument make an unreasonable assumption that high SF causes high HD, but it also assumes that the converse of this statement would be true – that is, low SF would cause low HD.

1. The evidence presented in premises 1 and 2 is about high SF and high blood cholesterol. Using this evidence to draw the conclusion that low SF would have the opposite effect to that of high SF is fallacious.

2. For example, the following statement is true: "high stress causes high blood pressure." However, the converse of this - "low stress causes low blood pressure" – is not true.

This is a 'Weaken EXCEPT' question. Therefore, four of the answer choices will weaken the argument. We will be looking for the single statement that does not weaken it.

Let us analyze the options one by one.

Answer choices explanation

[The bodily reactions of animal models to internal or external stimulants…] This option is incorrect. This statement does weaken the argument by suggesting that the use of premise 2 (which describes the bodily reaction of an animal model to high BC) to draw a conclusion about the bodily reaction of the humans to high BC may not be correct. Without this premise, the conclusion cannot hold.

[The per capita consumption of saturated fat in the United States has decreased…] This option is incorrect. This statement does weaken the argument by providing empirical evidence that in the same period in which SF decreased, HD increased by a lot more. This suggests that some factor, other than SF, causes HD and therefore disproves the causal assumptions that went into the drawing of the conclusion.

[An analysis of studies done on more than 600,000 men and women has…] This option is correct. This statement does not weaken the argument. From this statement, we learn some benefits of high blood cholesterol and risks of low blood cholesterol. However, the argument's main concern was not whether the overall impact of high blood cholesterol on human health is beneficial or not. The argument suggests only one specific effect of high blood cholesterol – that it causes heart disease. Likewise, the conclusion is only concerned about reducing HD. If reducing HD by reducing SF has some other side-effects (like increased risk of infections, as this option statement seems to suggest), then so be it. These are "other" side-effects and are outside the scope of the argument. The author is only claiming that reducing SF will reduce HD. He is not claiming that reducing SF will reduce the occurrence of all kinds of diseases.

[A study that covered more than 10,000 individuals has found…] This option is incorrect. This statement weakens the argument. It states that in humans, high blood cholesterol does not lead to HD. This directly disproves the subsidiary conclusion that can be drawn by combining premises 2 and 3 while also assuming that correlation implies causation, this subsidiary conclusion being that high blood cholesterol leads to HD.

[In a study where the dietary saturated fat consumption of young...] This option is incorrect. It weakens the argument. It shows that the extrapolation of premise 1 to all humans (as has been done in the argument) was incorrect. When females of a similar age-group and nationality as the men in the study that is cited in premise 1 ate a high SF diet, their blood cholesterol did not increase. This suggests that there is not a simple causal link between high SF and high BC. The chain of causations on which the conclusion rests therefore stands broken.