The following classic errors of reasoning appear with some frequency. The
review is given in layman’s, not philosophical, terms:
Uncertain Use of a Term or Concept
As an argument progresses, the author must use each term in a constant,
coherent fashion. Using a term in different ways is inherently confusing and
undermines the integrity of the argument. Here is an example:
“Some people claim that the values that this country was built on are
now being ignored by modern-day corporations. But this is incorrect.
Corporations are purely profit-driven enterprises, beholden only to their
shareholders, and as such they can only assess objects based on their
value.”
The term “value” is used in the example above in two different senses: first in a
moral or ethical sense and then in a monetary sense. This shift in meaning
undermines the author’s position.
This type of answer choice appears more frequently as an incorrect answer than
any other type. Here are examples of how this error of reasoning is described in
LSAT answer choices:
“depending on the ambiguous use of a key term”
“it confuses two different meanings of the word ‘solve’ ”
“relies on interpreting a key term in two different ways”
“equivocates with respect to a central concept”
“allows a key term to shift in meaning from one use to the next”
“fails to define the term”
Source Argument
Also known as an ad hominem, this type of flawed argument attacks the person
(or source) instead of the argument they advance. Because the LSAT is
concerned solely with argument forms, a speaker can never validly attack the
character or motives of a person; instead, a speaker must always attack the
argument advanced by a person. Here is an example:
“The anti-smoking views expressed by Senator Smith should be
ignored. After all, Smith himself is a smoker!”
A source argument can take different forms, including the following:
1. Focusing on the motives of the source.
2. Focusing on the actions of the source (as in the above example).
In the real world, you will often hear source arguments used by children and
politicians (the two being alike in a number of ways, of course).
Here are examples of how this error of reasoning is described in LSAT answer
choices:
“makes an attack on the character of opponents”
“it is directed against the proponent of a claim rather than against the
claim itself”
“he directs his criticism against the person making the argument rather
than directing it against the argument itself”
“it draws conclusions about the merit of a position and about the content
of that position from evidence about the position’s source”
“assuming that a claim is false on the grounds that the person defending
it is of questionable character”
Circular Reasoning
In circular reasoning the author assumes as true what is supposed to be proved.
Consider the following example:
“This essay is the best because it is better than all the others.”
In this example the premise and the conclusion are identical in meaning. As we
know, the conclusion should always follow from the premise. In the example
above, the premise supports the conclusion, but the conclusion equally supports
the premise, creating a “circular” situation where you can move from premise to
conclusion, and then back again to the premise, and so on. Here is another
example: “I must be telling the truth because I’m not lying.”
Here are examples of how this error of reasoning is described in LSAT answer
choices:
“it assumes what it seeks to establish”
“argues circularly by assuming the conclusion is true in stating the
premises”
“presupposes the truth of what it sets out to prove”
“the argument assumes what it is attempting to demonstrate”
“it takes for granted the very claim that it sets out to establish”
“it offers, in place of support for its conclusion, a mere restatement of
that conclusion”
Errors of Conditional Reasoning
