Formal logic is a skill that is very important, and highly tested, on the LSAT. Formal logic will appear in three of the four scored sections of the exam. First, formal logic appears in almost every analytical reasoning, which is known as logic games, question. Second, formal logic appears in a variety of question types within the logical reasoning section of the exam as well.
Furthermore, formal logic is a skill that a student can use one time, and then simply discard after taking the LSAT. In order to “think like a lawyer,” a term you are likely to hear too often during you 1L year, you must be able to effectively apply formal logic to various laws and facts. So, this learning this skill for the LSAT is just the beginning of your formal logic training and education. This is likely why this skill is so critical for LSAT success, because after all, the LSAT is advertised as testing the skills necessary to succeed in law school!
Here is an example of formal logic in a logical reasoning format that does not require a law degree to understand.
If I were to say “all law school books are expensive books”, you would be correct in knowing that if you buy a law school book, it will be expensive.
However, we know nothing absolute about expensive books. So, if you were to reply, “this book is expensive,” I could not be certain that the book you were speaking about is a law school book. For all I know, it may be another, ancient collector book about art or the Roman Empire.
So, the all preceding “law school books” is sufficient to establish that the book is an “expensive book.” The key is to not focus on the statement, because who cares whether or not you agree with what the author wrote, but rather to focus on the logic underlying the statement. If you can remain disconnected and seek out the formal logic, you will not be led astray.