Assumptions and Conditionality

Problems containing conditional reasoning tend to produce two types of
assumption answer choices:
1. If conditional statements are linked together in the argument, the correct
answer choice for an Assumption question will typically supply a
missing link in the chain, as in the following example:
Premises: A----------> B------------> C
Conclusion: A-------------> D
Assumption: C-----------> D (or the contrapositive)
Thus, if you encounter linked statements and an Assumption question,
be prepared to supply the missing link or the contrapositive of that link.
2. The assumption underlying a conditional statement is that the necessary
condition must occur in order for the sufficient condition to occur. Thus,
the author always assumes that any statement that would challenge the
truth of the relationship is false. If no conditional chains are present and
only a conditional conclusion exists, the correct answer will usually
deny scenarios where the sufficient condition occurs and the necessary
does not. In other words, the assumption in these arguments always
protects the necessary condition (that is, it works as a Defender). If you
see a conditional conclusion and then are asked an Assumption
question, immediately look for an answer that confirms that the
necessary condition is truly necessary or that eliminates possible
alternatives to the necessary condition.
Please take a moment to complete the following problem:
3. Emissions from automobiles that burn gasoline and
automobiles that burn diesel fuel are threatening the
quality of life on our planet, contaminating both
urban air and global atmosphere. Therefore, the only
effective way to reduce such emissions is to replace
the conventional diesel fuel and gasoline used in
automobiles with cleaner-burning fuels, such as
methanol, that create fewer emissions.
Which one of the following is an assumption on
which the argument depends?
(A) Reducing the use of automobiles would not
be a more effective means to reduce
automobile emissions than the use of
methanol.
(B) There is no fuel other than methanol that is
cleaner-burning than both diesel fuel and
gasoline.
(C) If given a choice of automobile fuels,
automobile owners would not select
gasoline over methanol.
(D) Automobile emissions constitute the most
serious threat to the global environment.
(E) At any given time there is a direct correlation
between the level of urban air pollution and
the level of contamination present in the
global atmosphere.
The last sentence contains the conclusion of the argument, which is conditional
(note the use of the necessary condition indicator “only”):
ERE = Effectively reduce emissions
Replace = Replace the conventional diesel fuel and gasoline used in
automobiles with cleaner-burning fuels, such as methanol,
that create fewer emissions.
ERE------------> Replace
According to the author, to effectively reduce emissions, conventional fuels
must be replaced. Based on our discussion, since the stimulus does not present
any conditional chains, you should look for an answer that protects the
necessary condition. Answer choice (A) is a Defender that does just that,
eliminating an idea that would undermine the relationship.
Answer choice (A): This is the correct answer. Consider the author’s position
that the only effective way to reduce emissions is fuel replacement. Wouldn’t it
be more effective to simply stop using cars altogether? Of course this is true, but
this would undermine the conditional nature of the conclusion and so the author
assumes that this possibility cannot occur.
If this answer is troubling you, use the Assumption Negation Technique and ask
yourself if the following statement would undermine the argument:
Reducing the use of automobiles would be a more effective means to
reduce automobile emissions than the use of methanol.
This answer clearly shows that there are other, more effective ways of reducing
emissions and therefore the answer attacks the argument. This must be the
correct answer.
Answer choice (B): The author is not committed to methanol because the
stimulus clearly references “fuels such as methanol.” Accordingly, this answer is
not an assumption of the argument.
Answer choice (C): The choices automobile owners would make are not part of
the argument made by the author. The author simply states that the only
effective way to achieve reduced emissions is fuel replacement. No assumption
is made about whether automobile owners would follow that way. The problem
with the answer can be highlighted by this example:
An argument is made that the best way to achieve long-lasting fame is to
commit suicide. Does the author assume that people will or will not
choose that path? No, because the best way does not involve an
assumption about how people will actually act.
Answer choice (D): This answer falls under the second of the three quirks
discussed in the previous section. The author clearly believes that automobile
emissions are a serious threat to the environment, but this does not mean that the
author has assumed they are the most serious threat. Negate the answer and ask
yourself, “What would the author say to the negation?” The author would reply
that he or she never indicated that emissions were the most serious threat, so it is
fine that they are not.
Answer choice (E): We know that both urban air and the global atmosphere are
contaminated by cars, but the author does not indicate that there is a direct
correlation between the two. This answer, when negated, has no effect on the
argument (and must therefore be incorrect).