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LSAT Formal Logic

This series of lesson articles will deal with LSAT Formal Logic. Learning some tricks for handling LSAT Formal Logic can translate into some quick points on test day. This lesson series covers the following articles:

LSAT Formal Logic: An Introduction
LSAT If-Then Statements
LSAT Contrpositive 
Best LSAT Logic Tip

LSAT Formal Logic

The LSAT doesn’t explicitly test formal logic in many Logical Reasoning questions; however, your ability to analyze argument structure often depends on your understanding of some basic formal principles. Furthermore, the Analytical Reasoning section is based entirely in formal logic.

This lesson forms the foundation for your understanding of formal logic. As you practice with the TestSherpa lessons and tests and released LSAC PrepTests, learn to recognize the formal structures hidden in many casual arguments. You can often paraphrase a difficult question stimulus into small, easy to understand formal statements.

LSAT Formal Logic Conditional Statements

The basic unit of the formal logic contained in the LSAT is the conditional statement. The conditional statement asserts that if A is true, B must also be true.

When looking at the statement “if A then B,” A is called the antecedent (because it comes first), and B is called the consequent (because it is the result if A happens). The LSAT won’t test you on these names, but it’s easier to talk about LSAT formal logic if you know what they mean.

The conditional statement can take many forms:

If I drop the egg, it will break.

If I am late for class, then my professor will fail me.

When Tommy gets sick, he likes to eat soup.

All monkeys eat bananas.

If I don’t get a raise, I’m going to quit.

All conditional statements can be paraphrased in the following form. (By the way, did you notice that the previous sentence is also a conditional statement in its own right?)

If A then B

or more simply (and easier to write in your test booklet)

A –> B

For example: If I drop the egg, it will break.
Paraphrase: If drop then break. Or you could write: D –> B

If I am late for class, then my professor will fail me.

Paraphrase: If late then fail. Or you could write:  L –> F

When Tommy gets sick, he likes to eat pineapples.

Paraphrase: If sick then pineapples. Or you could write:  S –> P

All monkeys eat bananas.

Paraphrase: If monkey then banana. Or you could write:  M –> B

If I don’t get a raise, I’m going to quit.

Paraphrase: If not raise then quit. Or you could write:  R –> Q

Learning to write and understand the short hand with the arrows can really save you some time on test day.

The next article in our series on LSAT Formal Logic goes into more detail on LSAT If-Then Statements.

This Post Has One Comment
  1. Hello, and thank you very much for all of the help. I wouldn’t have understood this as well as I do now without the help of this site (which was actually referred to me by my lsat professor.) Thanks so much! :)

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