We typically use the term “new” or “rogue” to refer to an element that appears only in
the conclusion or only in a premise.
If you see a weakness in the argument, look for an answer that eliminates the weakness
or assumes that it does not exist. In other words, close the gaps in the argument.
Supporter answer choices lend themselves well to prephrasing. Defender answers do not
because there are too many possibilities to choose from.
Most LSAT publications and courses present a limited description of
assumptions. An assumption is described solely as a linking statement, one that
links two premises or links a premise to the conclusion. If no other description
of assumptions is given, this limited presentation cheats students of the
possibility of fully understanding the way assumptions work within arguments
and the way they are tested by the makers of the exam.
On the LSAT, assumptions play one of two roles—the Supporter or the
Defender. The Supporter role is the traditional linking role, where an
assumption connects the pieces of the argument. Consider the following
example:
All male citizens of Athens had the right to vote. Therefore, Socrates
had the right to vote in Athens.
The linking assumption is that Socrates was a male citizen of Athens. This
connects the premise element of male citizens having the right to vote and the
conclusion element that Socrates had the right to vote (affiliated assumptions are
“Socrates was male” and “Socrates was a citizen of Athens”).
Because Supporters often connect “new” or “rogue” pieces of information in
the argument, the Supporter role generally appears similar to the Justify the
Conclusion answers discussed in the previous section. In fact, a number of
correct Justify the Conclusion answers are assumptions of the argument,
especially when the argument contains a conditional structure. This is actually a
benefit because if you mis-identify a Justify question as an Assumption question
there is still a reasonable possibility that you can answer the question correctly.
Supporter assumptions on the LSAT are often relatively easy for students to
identify because they can see the gap in the argument. The Supporter
assumption, by definition, closes the hole by linking the elements together.
Should you ever see a gap or a new element in the conclusion, a Supporter
assumption answer will almost certainly close the gap or link the new element
back to the premises.
The Defender role is entirely different, and Defender assumptions protect the
argument by eliminating ideas that could weaken the argument. Consider our
discussion from Chapter Two:
“When you read an LSAT argument from the perspective of the author,
keep in mind that he or she believes that their argument is sound. In
other words, they do not knowingly make errors of reasoning. This is a
fascinating point because it means that LSAT authors, as part of the
LSAT world, function as if the points they raise and the conclusions
they make have been well-considered and are airtight.”
By assuming that any threat to the argument does not exist, the author can present the
argument and claim it is valid. If the author knew of imperfections and still presented the
argument without a caveat, then the author would be hard-pressed to claim that this
conclusion— especially an absolute one— was reasonable.
This fundamental truth of the LSAT has a dramatic impact when you consider
the range of assumptions that must be made by an LSAT author. In order to
believe the argument is “well-considered and airtight,” an author must assume
that every possible objection has been considered and rejected. Consider the
following causal argument:
People who read a lot are more intelligent than other people. Thus,
reading must cause a person to be intelligent.
Although the conclusion is questionable (for example, the situation may be
reversed: intelligence might be the cause of reading a lot), in the author’s mind
all other alternative explanations are assumed not to exist. Literally, the author
assumes that any idea that would weaken the argument is impossible and cannot
occur. Consider some of the statements that would attack the conclusion above:
Sleeping more than eight hours causes a person to be intelligent.
Regular exercise causes a person to be intelligent.
A high-protein diet causes a person to be intelligent.
Genetics cause a person to be intelligent.
Each of these ideas would undermine the conclusion, but they are assumed by
the author not to be possible, and the author therefore makes the following
assumptions in the original argument:
the conclusion or only in a premise.
If you see a weakness in the argument, look for an answer that eliminates the weakness
or assumes that it does not exist. In other words, close the gaps in the argument.
Supporter answer choices lend themselves well to prephrasing. Defender answers do not
because there are too many possibilities to choose from.
Most LSAT publications and courses present a limited description of
assumptions. An assumption is described solely as a linking statement, one that
links two premises or links a premise to the conclusion. If no other description
of assumptions is given, this limited presentation cheats students of the
possibility of fully understanding the way assumptions work within arguments
and the way they are tested by the makers of the exam.
On the LSAT, assumptions play one of two roles—the Supporter or the
Defender. The Supporter role is the traditional linking role, where an
assumption connects the pieces of the argument. Consider the following
example:
All male citizens of Athens had the right to vote. Therefore, Socrates
had the right to vote in Athens.
The linking assumption is that Socrates was a male citizen of Athens. This
connects the premise element of male citizens having the right to vote and the
conclusion element that Socrates had the right to vote (affiliated assumptions are
“Socrates was male” and “Socrates was a citizen of Athens”).
Because Supporters often connect “new” or “rogue” pieces of information in
the argument, the Supporter role generally appears similar to the Justify the
Conclusion answers discussed in the previous section. In fact, a number of
correct Justify the Conclusion answers are assumptions of the argument,
especially when the argument contains a conditional structure. This is actually a
benefit because if you mis-identify a Justify question as an Assumption question
there is still a reasonable possibility that you can answer the question correctly.
Supporter assumptions on the LSAT are often relatively easy for students to
identify because they can see the gap in the argument. The Supporter
assumption, by definition, closes the hole by linking the elements together.
Should you ever see a gap or a new element in the conclusion, a Supporter
assumption answer will almost certainly close the gap or link the new element
back to the premises.
The Defender role is entirely different, and Defender assumptions protect the
argument by eliminating ideas that could weaken the argument. Consider our
discussion from Chapter Two:
“When you read an LSAT argument from the perspective of the author,
keep in mind that he or she believes that their argument is sound. In
other words, they do not knowingly make errors of reasoning. This is a
fascinating point because it means that LSAT authors, as part of the
LSAT world, function as if the points they raise and the conclusions
they make have been well-considered and are airtight.”
By assuming that any threat to the argument does not exist, the author can present the
argument and claim it is valid. If the author knew of imperfections and still presented the
argument without a caveat, then the author would be hard-pressed to claim that this
conclusion— especially an absolute one— was reasonable.
This fundamental truth of the LSAT has a dramatic impact when you consider
the range of assumptions that must be made by an LSAT author. In order to
believe the argument is “well-considered and airtight,” an author must assume
that every possible objection has been considered and rejected. Consider the
following causal argument:
People who read a lot are more intelligent than other people. Thus,
reading must cause a person to be intelligent.
Although the conclusion is questionable (for example, the situation may be
reversed: intelligence might be the cause of reading a lot), in the author’s mind
all other alternative explanations are assumed not to exist. Literally, the author
assumes that any idea that would weaken the argument is impossible and cannot
occur. Consider some of the statements that would attack the conclusion above:
Sleeping more than eight hours causes a person to be intelligent.
Regular exercise causes a person to be intelligent.
A high-protein diet causes a person to be intelligent.
Genetics cause a person to be intelligent.
Each of these ideas would undermine the conclusion, but they are assumed by
the author not to be possible, and the author therefore makes the following
assumptions in the original argument:
