Premise and Conclusion Analysis Drill
Question #1. Stimulus drawn from the October 2002 LSAT.
Conclusion: From these contradictory opinions, we see that experts are useless for guiding one’s
decisions about one’s health.
Premise: Every year, new reports appear concerning the health risks posed by certain substances,
such as coffee and sugar.
Premise: One year an article claimed that coffee is dangerous to one’s health.
Premise: The next year, another article argued that coffee has some benefits for one’s health.
The conclusion is introduced by the phrase “we see that.”
The argument is weak. The conclusion is far too strong in saying that “experts are useless.” Just because
the different articles about substances disagree does not prove that experts cannot help you with your
health (a much broader field than the substances cover). In addition, the articles about coffee could have
covered differing aspects of coffee, some of which are beneficial and some of which are detrimental.
Question #2. Stimulus drawn from the October 2002 LSAT.
Conclusion: The incentive of grades, therefore, serves no essential academic purpose.
Premise: Some teachers claim that students would not learn curricular content without the
incentive of grades.
Premise: But students with intense interest in the material would learn it without this incentive,
while the behavior of students lacking all interest in the material is unaffected by such an
incentive.
The conclusion contains the conclusion indicator, “therefore.” Note also the use of the “Some teachers
claim...” device discussed earlier in the chapter. This construction raises a viewpoint that the author
eventually argues against.
The argument is weak. When discussing the students, the author makes the mistake of discussing only
the extremes—those with intense interest and those lacking all interest. No effort is made to address the
students who fall between these extremes.
Question #3. Stimulus drawn from the October 2002 LSAT.
Conclusion: Building a dam would yield no overall gain in agricultural productivity in the region
as a whole.
Premise: Damming the Merv River would provide irrigation for the dry land in its upstream
areas.
Premise: Unfortunately, a dam would reduce agricultural productivity in the fertile land
downstream by reducing the availability and quality of water there.
Premise: The productivity loss in the downstream area would be greater than the productivity
gain upstream.
The conclusion is introduced in the last sentence by the indicator “so.”
The argument is strong. The author discusses both the upstream and downstream areas, showing that the
gain from the dam in the upstream area would not offset the loss of productivity in the downstream area.
In fact, it appears an even stronger conclusion would be warranted, such as “building a dam would yield
an overall loss of productivity. Since the author directly addresses overall productivity, possible
objections about acreage and volume produced are rendered moot. The author even goes so far as to
indicate that the downstream land is fertile, deflecting another possible objection about the work
involved in making the land productive.
Note that this is a good example of a fantasy stimulus, one that is based on a scenario that does not exist
in the real world. There is no “Merv River” anywhere in the world (although there was an ancient city of
Merv in Turkmenistan). Stimuli like this one are often created to portray a certain reasoning form or
situation. While fantasy stimuli are often obvious (containing fake countries, etc.), you should not
approach them any differently than real-world, fact-based stimuli because Logical Reasoning is about
argumentation, and argumentation can be portrayed equally well in real world or fantasy stimuli.
Question #4. Stimulus drawn from the June 2002 LSAT.
Premise: In a study, infant monkeys given a choice between two surrogate mothers—a bare wire
structure equipped with a milk bottle, or a soft, suede-covered wire structure equipped
with a milk bottle—unhesitatingly chose the latter.
Premise: When given a choice between a bare wire structure equipped with a milk bottle and a
soft, suede-covered wire structure lacking a milk bottle, they unhesitatingly chose the
former.
Careful! The stimulus is only a fact set and does not contain a conclusion. Therefore, there is no
argument present and no evaluation of argument validity can be made.
Question #5. Stimulus drawn from the December 2001 LSAT.
Conclusion: This is conclusive evidence that psychoses, unlike neuroses, have nothing to do with
environmental factors but rather are caused by some sort of purely organic condition, such
as abnormal brain chemistry or brain malformations.
Premise: While it was once believed that the sort of psychotherapy appropriate for the treatment
of neuroses caused by environmental factors is also appropriate for schizophrenia and
other psychoses, it is now known that these latter, more serious forms of mental
disturbance are best treated by biochemical—that is, medicinal—means.
The conclusion is introduced by the phrase “this is conclusive evidence that.”
The argument is weak. Again, the language used by the author is too strong—“nothing to do with
environmental factors”—for the evidence provided by the premises. Nowhere in the argument has the
author proven beyond a shadow of doubt that environmental factors do not play a role in neuroses.
Question #6. Stimulus drawn from the December 2000 LSAT.
Conclusion: Thus, if relativity theory is correct, either quantum mechanics’ prediction about
tachyons is erroneous or tachyons travel backwards in time.
Premise: If relativity theory is correct, no object can travel forward in time at a speed greater than
the speed of light.
Premise: Yet quantum mechanics predicts that the tachyon, a hypothetical subatomic particle,
travels faster than light.
The conclusion is introduced by the indicator “thus.” The second premise is actually a counter-premise
introduced by the indicator “yet.”
The argument is strong. Note how the author qualifies the conclusion, using the phrase “if relativity
theory is correct.” This qualifying phase makes the argument easier to defend because it protects against
the possibility that relativity theory is wrong (if relativity theory is wrong, the author’s conclusion does
not apply). Note the conclusion concerning travelling backwards in time as the other possibility is set up
by the fact that quantum theory predicts that no object can travel forward in time at a speed greater than
the speed of light. If an object cannot travel forward in time, then it must travel backwards (time does not
stop, of course, so those are the only two options).
Question #7. Stimulus drawn from the December 2002 LSAT.
Conclusion: Any student, whatever his or her major, will be served well in later life by taking any
philosophy course.
Premise: Any course that teaches students how to write is one that will serve them well later in
life.
Premise: Some philosophy courses teach students how to write.
The conclusion is introduced by the device “therefore, since” and in this case the inserted premise is
quite lengthy.
The argument is weak. Although the premise indicates that some philosophy courses teach students how
to write, the conclusion goes too far in saying students will be served well in later life by taking any
philosophy course.
Question #8. Stimulus drawn from the October 1999 LSAT.
Conclusion: This characteristic [altering the environment] is actually quite common
Premise: It is well known that many species adapt to their environment, but it is usually assumed
that only the most highly evolved species alter their environment in ways that aid their
own survival.
Premise: Certain species of plankton, for example, generate a gas that is converted in the
atmosphere into particles of sulfate.
Premise: These particles cause water vapor to condense, thus forming clouds.
Premise: Indeed, the formation of clouds over the ocean largely depends on the presence of these
particles.
Premise: More cloud cover means more sunlight is reflected, and so the Earth absorbs less heat.
Premise: Thus plankton cause the surface of the Earth to be cooler and this benefits the plankton.
This argument is hard to absorb because the subject matter is challenging and the structure is complex.
The main conclusion is actually the second sentence. There is another conclusion in the argument, in the
last sentence, but this is a sub-conclusion. This sub-conclusion appears in the plankton example, and like
all examples, it is used to illustrate the main conclusion.
The argument is strong. A viewpoint is presented (that it is thought that only highly evolved species alter
their environment) and then this viewpoint is disputed with the example of a simple organism that changes
its environment. Although the author has not proven undeniably that the characteristic is “quite common”
(this would require more examples), the author has successfully shown that non-highly evolved species
exhibit that characteristic, making it likely that the characteristic appears in other species.
Question #1. Stimulus drawn from the October 2002 LSAT.
Conclusion: From these contradictory opinions, we see that experts are useless for guiding one’s
decisions about one’s health.
Premise: Every year, new reports appear concerning the health risks posed by certain substances,
such as coffee and sugar.
Premise: One year an article claimed that coffee is dangerous to one’s health.
Premise: The next year, another article argued that coffee has some benefits for one’s health.
The conclusion is introduced by the phrase “we see that.”
The argument is weak. The conclusion is far too strong in saying that “experts are useless.” Just because
the different articles about substances disagree does not prove that experts cannot help you with your
health (a much broader field than the substances cover). In addition, the articles about coffee could have
covered differing aspects of coffee, some of which are beneficial and some of which are detrimental.
Question #2. Stimulus drawn from the October 2002 LSAT.
Conclusion: The incentive of grades, therefore, serves no essential academic purpose.
Premise: Some teachers claim that students would not learn curricular content without the
incentive of grades.
Premise: But students with intense interest in the material would learn it without this incentive,
while the behavior of students lacking all interest in the material is unaffected by such an
incentive.
The conclusion contains the conclusion indicator, “therefore.” Note also the use of the “Some teachers
claim...” device discussed earlier in the chapter. This construction raises a viewpoint that the author
eventually argues against.
The argument is weak. When discussing the students, the author makes the mistake of discussing only
the extremes—those with intense interest and those lacking all interest. No effort is made to address the
students who fall between these extremes.
Question #3. Stimulus drawn from the October 2002 LSAT.
Conclusion: Building a dam would yield no overall gain in agricultural productivity in the region
as a whole.
Premise: Damming the Merv River would provide irrigation for the dry land in its upstream
areas.
Premise: Unfortunately, a dam would reduce agricultural productivity in the fertile land
downstream by reducing the availability and quality of water there.
Premise: The productivity loss in the downstream area would be greater than the productivity
gain upstream.
The conclusion is introduced in the last sentence by the indicator “so.”
The argument is strong. The author discusses both the upstream and downstream areas, showing that the
gain from the dam in the upstream area would not offset the loss of productivity in the downstream area.
In fact, it appears an even stronger conclusion would be warranted, such as “building a dam would yield
an overall loss of productivity. Since the author directly addresses overall productivity, possible
objections about acreage and volume produced are rendered moot. The author even goes so far as to
indicate that the downstream land is fertile, deflecting another possible objection about the work
involved in making the land productive.
Note that this is a good example of a fantasy stimulus, one that is based on a scenario that does not exist
in the real world. There is no “Merv River” anywhere in the world (although there was an ancient city of
Merv in Turkmenistan). Stimuli like this one are often created to portray a certain reasoning form or
situation. While fantasy stimuli are often obvious (containing fake countries, etc.), you should not
approach them any differently than real-world, fact-based stimuli because Logical Reasoning is about
argumentation, and argumentation can be portrayed equally well in real world or fantasy stimuli.
Question #4. Stimulus drawn from the June 2002 LSAT.
Premise: In a study, infant monkeys given a choice between two surrogate mothers—a bare wire
structure equipped with a milk bottle, or a soft, suede-covered wire structure equipped
with a milk bottle—unhesitatingly chose the latter.
Premise: When given a choice between a bare wire structure equipped with a milk bottle and a
soft, suede-covered wire structure lacking a milk bottle, they unhesitatingly chose the
former.
Careful! The stimulus is only a fact set and does not contain a conclusion. Therefore, there is no
argument present and no evaluation of argument validity can be made.
Question #5. Stimulus drawn from the December 2001 LSAT.
Conclusion: This is conclusive evidence that psychoses, unlike neuroses, have nothing to do with
environmental factors but rather are caused by some sort of purely organic condition, such
as abnormal brain chemistry or brain malformations.
Premise: While it was once believed that the sort of psychotherapy appropriate for the treatment
of neuroses caused by environmental factors is also appropriate for schizophrenia and
other psychoses, it is now known that these latter, more serious forms of mental
disturbance are best treated by biochemical—that is, medicinal—means.
The conclusion is introduced by the phrase “this is conclusive evidence that.”
The argument is weak. Again, the language used by the author is too strong—“nothing to do with
environmental factors”—for the evidence provided by the premises. Nowhere in the argument has the
author proven beyond a shadow of doubt that environmental factors do not play a role in neuroses.
Question #6. Stimulus drawn from the December 2000 LSAT.
Conclusion: Thus, if relativity theory is correct, either quantum mechanics’ prediction about
tachyons is erroneous or tachyons travel backwards in time.
Premise: If relativity theory is correct, no object can travel forward in time at a speed greater than
the speed of light.
Premise: Yet quantum mechanics predicts that the tachyon, a hypothetical subatomic particle,
travels faster than light.
The conclusion is introduced by the indicator “thus.” The second premise is actually a counter-premise
introduced by the indicator “yet.”
The argument is strong. Note how the author qualifies the conclusion, using the phrase “if relativity
theory is correct.” This qualifying phase makes the argument easier to defend because it protects against
the possibility that relativity theory is wrong (if relativity theory is wrong, the author’s conclusion does
not apply). Note the conclusion concerning travelling backwards in time as the other possibility is set up
by the fact that quantum theory predicts that no object can travel forward in time at a speed greater than
the speed of light. If an object cannot travel forward in time, then it must travel backwards (time does not
stop, of course, so those are the only two options).
Question #7. Stimulus drawn from the December 2002 LSAT.
Conclusion: Any student, whatever his or her major, will be served well in later life by taking any
philosophy course.
Premise: Any course that teaches students how to write is one that will serve them well later in
life.
Premise: Some philosophy courses teach students how to write.
The conclusion is introduced by the device “therefore, since” and in this case the inserted premise is
quite lengthy.
The argument is weak. Although the premise indicates that some philosophy courses teach students how
to write, the conclusion goes too far in saying students will be served well in later life by taking any
philosophy course.
Question #8. Stimulus drawn from the October 1999 LSAT.
Conclusion: This characteristic [altering the environment] is actually quite common
Premise: It is well known that many species adapt to their environment, but it is usually assumed
that only the most highly evolved species alter their environment in ways that aid their
own survival.
Premise: Certain species of plankton, for example, generate a gas that is converted in the
atmosphere into particles of sulfate.
Premise: These particles cause water vapor to condense, thus forming clouds.
Premise: Indeed, the formation of clouds over the ocean largely depends on the presence of these
particles.
Premise: More cloud cover means more sunlight is reflected, and so the Earth absorbs less heat.
Premise: Thus plankton cause the surface of the Earth to be cooler and this benefits the plankton.
This argument is hard to absorb because the subject matter is challenging and the structure is complex.
The main conclusion is actually the second sentence. There is another conclusion in the argument, in the
last sentence, but this is a sub-conclusion. This sub-conclusion appears in the plankton example, and like
all examples, it is used to illustrate the main conclusion.
The argument is strong. A viewpoint is presented (that it is thought that only highly evolved species alter
their environment) and then this viewpoint is disputed with the example of a simple organism that changes
its environment. Although the author has not proven undeniably that the characteristic is “quite common”
(this would require more examples), the author has successfully shown that non-highly evolved species
exhibit that characteristic, making it likely that the characteristic appears in other species.
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