Introduction to logical reasoning - Understanding argument s...

Learning Outcomes

After reading this article, you will be able to:

• Identify and distinguish the core elements of arguments: premises and conclusions.
• Recognize common logical indicators and their relevance for the LSAT.
• Understand and define the role of assumptions in arguments.
• Apply these principles to tackle LSAT-style questions requiring argument analysis.

LSAT Syllabus

For LSAT, you are required to understand argument structure and the skills related to logical reasoning. For efficient revision, focus on:

• Identifying premises and conclusions within arguments.
• Understanding logical indicator words (such as “because,” “therefore,” “since,” “thus”).
• Recognizing the role and necessity of assumptions in arguments.
• Differentiating between necessary and sufficient statements.
• Applying argument structure knowledge across all LSAT logical reasoning question types.

Test Your Knowledge

Attempt these questions before reading this article. If you find some difficult or cannot remember the answers, remember to look more closely at that area during your revision.

1. Which of these best indicates a premise?
   1. since
   2. therefore
   3. so
   4. consequently
2. Which of these statements describes an assumption most accurately?
   1. It is always stated directly in the text
   2. It must be true for the argument’s reasoning to function
   3. It never influences the conclusion
   4. It is the same as a premise

3. What does the word “thus” typically signal in an argument?

4. True or false: An argument always contains a conclusion.

Introduction

A fundamental skill for LSAT logical reasoning is the ability to break down arguments into their essential components. Understanding argument structure—how premises support a conclusion, and where assumptions lie—is a prerequisite for success in all LSAT logical reasoning questions. Arguments in LSAT questions use ordinary language but demand careful and critical reading.

Key Term: argument
An argument consists of a conclusion (a claim the author wants you to accept) and one or more premises (supporting statements offered as reasons for that conclusion).

Premises

Premises supply evidence or reasons for the argument’s claim. They are usually presented as statements or facts the author wants you to accept.

Key Term: premise
A premise is a statement that serves as evidence or a reason supporting a conclusion. LSAT premise indicators include: "since," "because," "given that," "as," and "for."

Conclusions

A conclusion is the central claim that the author wishes you to accept, based on the premises. It is the destination that the author’s reasoning tries to establish.

Key Term: conclusion
The conclusion is the main point or claim in an argument. Common indicators: "therefore," "thus," "so," "hence," "consequently," and "it follows that."

Assumptions

Every argument relies on at least one implicit assumption, whether or not it is explicitly stated. An assumption fills any gap between premise(s) and conclusion, often forming the weakest part of the argument.

Key Term: assumption
An assumption is an unstated but necessary idea or principle for the argument's reasoning to be valid. Removing the assumption breaks the logical chain between premises and conclusion.

Worked Example 1.1

A passage states:
"Studies show that people who commute by bicycle are healthier than car commuters. Therefore, to improve citywide health, everyone should be encouraged to cycle to work."

Question: What are the premises and the conclusion?

Answer:
Premise: "Studies show that people who commute by bicycle are healthier than car commuters."
Conclusion: "To improve citywide health, everyone should be encouraged to cycle to work."

Common Logical Indicators

Certain words are used to signal that a statement is functioning as a premise or a conclusion. Recognizing these is essential for argument analysis.

Premise Indicators

• because
• since
• as
• given that
• for

Conclusion Indicators

• therefore
• thus
• so
• hence
• it follows that

Revision Tip When identifying conclusions, look for opinion words (e.g. "should," "must," "ought," "probably"), evaluative claims, or recommendations. They typically signal the author’s main point.

Necessary vs. Sufficient

In complex arguments, it is important to distinguish between necessary and sufficient reasoning:

Key Term: necessary condition
A condition that must be true for a particular outcome to occur, but alone does not guarantee the outcome.

Key Term: sufficient condition
A condition that, if true, guarantees the outcome, although the outcome could also happen for other reasons.

Worked Example 1.2

Argument:
"Whenever Carla eats peanuts, she gets an allergic reaction. Carla has an allergic reaction. Therefore, Carla must have eaten peanuts."

Question: What is wrong with this argument’s reasoning?

Answer:
The argument confuses a sufficient condition ("Carla eats peanuts" always leads to a reaction) with a necessary condition (there may be other causes of her reaction). The conclusion assumes peanuts are the only cause, which is unsupported.

The Role of Assumptions in LSAT Arguments

On the LSAT, many questions focus on either exposing, challenging, or confirming assumptions in an argument. Identifying the assumption is essential for solving “assumption,” “strengthen,” and “weaken” question types.

Exam Warning

Students often confuse necessary conditions with sufficient conditions. For LSAT questions, always check whether the condition must happen for the argument (necessary) or is enough by itself to cause the outcome (sufficient).

Worked Example 1.3

Argument:
"All successful lawyers read legal journals. Alex reads legal journals. Therefore, Alex will be a successful lawyer."

Question: Is the logic valid?

Answer:
No. The premise states that reading legal journals is necessary for being a successful lawyer, but it does not guarantee success. Alex’s reading habits may be insufficient if other factors are involved.

Facts versus Arguments

Not all LSAT stimuli are actual arguments; some comprise only a set of facts. Identifying whether you are dealing with an argument or a fact set is critical for answering "main point," "structure," or "inference" questions.

Key Term: fact set
A sequence of statements that describe information but do not contain a claim or conclusion to prove.

Worked Example 1.4

Consider:
"Lakeview High enrolls 500 students. The school has 40 teachers, and its average class size is 20."

Question: Is this an argument or a fact set?

Answer:
This is a fact set. There is description but no conclusion or claim that is being proven.

Summary

Key Point Checklist

This article has covered the following key knowledge points:

• The essential building blocks of an argument: premises, conclusions, assumptions.
• Standard logical indicator words to identify premises and conclusions.
• The critical difference between necessary and sufficient conditions.
• How to distinguish arguments from fact sets on the LSAT.

Key Terms and Concepts

• argument
• premise
• conclusion
• assumption
• necessary condition
• sufficient condition
• fact set