The Central Assumption of Causal Conclusions

Understanding this assumption is absolutely critical to your LSAT success. The
makers of the test will closely examine your knowledge of this idea, especially in
Strengthen and Weaken questions.
Understanding the assumption that is at the heart of a causal conclusion is
essential to knowing why certain answers will be correct or incorrect. Most
students assume that the LSAT makes basic assumptions that are similar to the
real world; this is untrue and is a dangerous mistake to make.
When we discuss causality in the real world, there is an inherent understanding
that a given cause is just one possible cause of the effect, and that there are other
causes that could also produce the same effect. This is reasonable because we
have the ability to observe a variety of cause and effect scenarios, and
experience shows us that different actions can have the same result. The makers
of the LSAT do not think this way. When an LSAT speaker concludes that one
occurrence caused another, that speaker also assumes that the stated cause is the
only possible cause of the effect and that consequently the stated cause will
always produce the effect. This assumption is incredibly extreme and farreaching,
and often leads to surprising answer choices that would appear
incorrect unless you understand this assumption. Consider the following
example:
Premise: Average temperatures are higher at the equator than in
any other area.
Premise: Individuals living at or near the equator tend to have
lower per-capita incomes than individuals living
elsewhere.
Conclusion: Therefore, higher average temperatures cause lower percapita
incomes.
This argument is a classic flawed causal argument wherein two premises with a
basic connection (living at the equator) are used as the basis of a conclusion that
states that the connection is such that one of the elements actually makes the
other occur. The conclusion is flawed because it is not necessary that the one
element caused the other to occur: the two could simply be correlated in some
way or the connection could be random.
In the real world, we would tend to look at an argument like the one above and
think that while the conclusion is possible, there are also other things that could
cause the lower per-capita income of individuals residing at or near the equator,
such as a lack of natural resources. This is not how speakers on the LSAT view
the relationship. When an LSAT speaker makes an argument like the one
above, he or she believes that the only cause is the one stated in the conclusion
and that there are no other causes that can create that particular effect. Why is
this the case? Because for an LSAT speaker to come to that conclusion, he or
she must have weighed and considered every possible alternative and then
rejected each one. Otherwise, why would the speaker draw the given
conclusion? In the final analysis, to say that higher average temperatures cause
lower per-capita incomes the speaker must also believe that nothing else could
be the cause of lower per-capita incomes.
Answer choices that otherwise appear irrelevant will suddenly be obviously correct
when you understand the central causal assumption.
Thus, in every argument with a causal conclusion that appears on the LSAT, the
speaker believes that the stated cause is in fact the only cause and all other
theoretically possible causes are not, in fact, actual causes. This is an incredibly
powerful assumption, and the results of this assumption are most evident in
Weaken, Strengthen, and Assumption questions. We will discuss this effect on
Strengthen and Assumption questions in a later chapter. Following is brief
analysis of the effect of this assumption on Weaken questions.