Logical Reasoning Question Types-Error Identification

Logical reasoning (arguments) error identification problems look very similar to logical reasoning (arguments) argument enhancement problems. They both share the common attribute of a proposed argument that does not fully work. The main difference is that while the arguments in logical reasoning (arguments) argument enhancement problems are salvageable (in fact, the examinee is asked to salvage them), the arguments posed in logical reasoning (arguments) error identification problems are hopeless and the examinee is required to identify the error.

As with many other types of logical reasoning (arguments) problems, one of the key struggles is to identify the type of logical reasoning (arguments) error identification problem confronting the examinee. There are several different types of logical reasoning (arguments) error identification problems that are seen often on the LSAT. Some of these commonly seen types include: (1) the illogical use of a sample, (2) conclusion drawn from the wrong definition of a term that can mean more than one thing, (3) misuse of numbers and percentages, (4) personal (ad hominem) attacks, (5) emotional pleas, (6) conclusions based on expert credentials, (7) making determinations about an entire group from a small sample or vice versa, and (8) circular arguments.

Further discussion is warranted on several of these frequently seen logical reasoning (arguments) error identification problems. Consider the illogical use of a sample. Here is an example:

The House Ways and Means Committee makes many budgetary recommendations to House of Representatives. This Committee recently recommended passage of a bill raising federal employees' wages. Because the House Ways and Means Committee acts for the benefit of the House of Representatives as a whole the House will pass the bill.

In this case, simply because a majority of the committee (sample) thinks that a bill should be passed does not mean that a majority of the House of Representatives (whole) think the bill should pass.

Consider this example that misapplies numbers and percentages to reach its conclusion:

In 1965, only 20% of the National Basketball Association was composed of African-American players. By 1990, this percentage had risen to 70%. Therefore, many more African-American players were in the National Basketball Association in 1990.

This is a little trickier. The flaw is that just because the percentage of African-American players increased does not necessarily mean that the number of African-American players increased. For example, if the overall number of players in the league in 1965 was 1000, then 200 were African-American. If the overall number of players in the league had shrunk to 200 in 1990, then there were only 140 African-American players. What makes a problem like this even trickier is the fact that this statement may be true. It is important for the examinee to realize that it is not the truth of the conclusion that is important, it is the accuracy of the logic that led to the conclusion that is being tested.

Finally, consider this example of circular reasoning:

The fire hydrant is always broken, because the hydrant never worked.

This statement may seem reasonable enough. However, consider the conclusion in isolation, "the fire hydrant is always broken." The evidence for this conclusion should state why this is the case. Here, the evidence that the "hydrant never worked" is simply a different way of stating the conclusion. Therefore, the reasoning is circular.