Argument Analysis

In logic, the terms “strong/ weak,” “good/ bad,” “valid/ invalid,” and “sound/unsound”
are used to evaluate arguments. For our purposes, “strong,” “good,” “valid,” and
“sound” will be interchangeable and all terms refer to the logical structure of the argument. The same holds true for “weak,” “bad,” “invalid,” and “unsound.”
Once you have determined that an argument is present and you have identified
the conclusion, you must determine if the argument is a good one or a bad one.
This leads to the third Primary Objective:
Primary Objective #3: If the stimulus contains an argument,
determine whether the argument is strong or weak.
An argument can be valid without being true. For example, the following has a
valid argument structure but is not “true” in a real world sense: “All birds can fly.
An ostrich is a bird. Therefore, an ostrich can fly.”
To determine the strength of the argument, consider the relationship between
the premises and the conclusion—do the premises strongly suggest that the
conclusion would be true? Does the conclusion feel like an inevitable result of
the premises? Or does the conclusion seem to go beyond the scope of the
information in the premises? How persuasive does the argument seem to you?
When evaluating argument validity, the question you must always ask yourself
is: Do the given facts support the conclusion?
To better understand this concept we will examine two sample arguments. The
following argument uses the fact set we used before, with the addition of a
conclusion:

“The Jacksonville area has just over one million residents. Cincinnati
has almost two million residents. The New York area has almost
twenty million residents. Therefore, we should move to Jacksonville.”
Questions such as the ones in posed in this paragraph suggest that the author
has made unwarranted assumptions while constructing the argument. We will
discuss assumptions in more detail later.
The last sentence contains the conclusion, and makes this an argument. Notice
how the presence of the conclusion causes you to react more strongly to the
stimulus. Now, instead of just reading a set of cold facts, you are forced to
consider whether the premises have proven the given conclusion. In this case
the author asks you to accept that a move to Jacksonville is in order based on
the population of the city. Do you think the author has proven this point?
When considering the above argument, most people simply accept the
premises as factually accurate. There is nothing wrong with this (and indeed in
the real world they are true). As mentioned moments ago, in LSAT
argumentation the makers of the test largely allow authors to put forth their
premises unchallenged. The test makers are far more concerned about whether
those premises lead to the conclusion presented. In the argument above, there
is no reason to doubt the accuracy of the premises, but even if we accept the
premises as accurate, we still do not have to accept the conclusion.
Most people reading the argument above would agree that the conclusion is
weak. Even though the premises are perfectly acceptable, by themselves they
do not prove that “we should move to Jacksonville.” The typical reader will
experience a host of reactions to the conclusion: Why Jacksonville—why not a
city that is even smaller? What is so important about population? What about
considerations other than population size? Because questions of this nature
point to flaws in the argument, we would classify the argument as a poor one.
That is, the premises do not prove the conclusion. As shown by this example,
the acceptability of the premises does not automatically make the conclusion
acceptable. The reverse is also true—the acceptability of the conclusion does
not automatically make the premises acceptable.
The following is an example of a strong argument:
“Trees that shed their foliage annually are deciduous trees. Black Oak
trees shed their leaves every year. Therefore, Black Oak trees are
deciduous. ”