Formal Logic Defined

Formal Logic, also known as Symbolic Logic, is defined by Webster’s as, “The study of the properties of
propositions and deductive reasoning by abstraction and analysis of the form rather than the content of
propositions under consideration.” That definition is quite a mouthful, but the important part is in the
middle: “reasoning by analysis and abstraction of form rather than the content.” LSAT Formal Logic is
quite simply a standard way of translating relationships into symbols and then making inferences from
those symbolized relationships. And, because certain combinations always yield the same inference
regardless of the underlying topic, a close study of the combinations that frequently appear allows LSAT
takers to move quickly and confidently when attacking Formal Logic problems.
Students interested in improving their Formal Logic skills sometimes wonder if taking a university-level
symbolic logic class in addition to an LSAT course is a good idea. While symbolic logic classes do help
improve your understanding of certain LSAT concepts, unfortunately these logic classes also contain a
wide variety of concepts that have no application to the LSAT. We feel your time would be better spent
studying LSAT problems than by taking a symbolic logic course. In our discussion below, we will focus
on presenting those areas of Formal Logic that are specifically applicable to the LSAT.
On the LSAT, the basis for Formal Logic relationships are terms such as “all,” “none,” “some,” and
“most.” Here is an example of how Formal Logic works, using a few of those terms:
First, we examine a statement containing Formal Logic:
“Every author works long hours, and if you work long hours you are never happy. Some
authors are female.”
Second, we swiftly translate the statement into a set of symbols representing the concepts and
relationships:
F some A---> LH <---> H
(where F = female, A = author, LH = long hours, and H = happy)
Third, we examine the symbolic notation and make additive inferences:
Inferences:
F some LH
F some H
A<---> H
Although the example above may appear daunting, with practice you will be able to translate the statement
into the notation and make the inferences rapidly and with certainty. Later in this section we will return to
the problem above and fully explain each inference, and in the following pages we will discuss each of the
general relationships above and the standardized inferences that follow from combining certain
relationships. By the end of this supplement you should not only understand how to diagram any Formal
Logic problem, but also how to make inferences quickly and efficiently from your diagram.