Introduction to logical reasoning - Types of reasoning (dedu...

Learning Outcomes

After reading this article, you will be able to distinguish deductive and inductive reasoning, describe their features within LSAT arguments, and recognize how each type is tested in LSAT Logical Reasoning questions. You will also be able to identify relevant keywords, common question stems, and employ strategies for analysing both deductive and inductive argument structures on the exam.

LSAT Syllabus

For LSAT, you are required to understand the core types of reasoning used in arguments. In your revision, focus on:

• identifying and defining deductive and inductive reasoning
• determining how arguments use deductive and inductive logic
• recognising key question stems in LSAT Logical Reasoning relating to both reasoning types
• distinguishing arguments that use general rules to draw specific conclusions from those that generalise from evidence or examples
• ensuring you can quickly spot which type of reasoning is present in the stimulus, and apply the right analytical approach

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 type of reasoning guarantees the truth of its conclusion if all premises are true?
   1. deductive
   2. inductive
2. Which of the following is a hallmark of inductive reasoning?
   1. moves from specific examples to general conclusions
   2. moves from general principles to specific conclusions

3. True or false? On the LSAT, inference questions can involve either deductive or inductive logic.

4. In LSAT arguments, which key word often signals an inductive generalisation?
   1. therefore
   2. most
   3. only if
   4. since

Introduction

When answering LSAT Logical Reasoning questions, you must analyse how the argument moves from premises to its conclusion. The two main types of reasoning you will encounter are deductive and inductive reasoning. Understanding their structure and how LSAT questions test each is fundamental to choosing correct answers under exam conditions.

Deductive Reasoning

Deductive reasoning claims that, if its premises are true, its conclusion is guaranteed to be true. It moves from general rules to particular cases and is used when the argument's logic is strictly valid.

Key Term: deductive reasoning
An argument structure where, if all premises are true, the conclusion must also be true; often moves from general rules to specific conclusions.

Deductive arguments on the LSAT often include conditional statements, quantifiers ("all", "none", "if...then"), and strict logic. For a deduction to be valid, it admits no exceptions.

Inductive Reasoning

Inductive reasoning relies on patterns, examples, or evidence, and draws a general or probable conclusion from the specifics. Here, the conclusion is likely or probable, not guaranteed, even if all premises are true.

Key Term: inductive reasoning
A form of reasoning that draws general conclusions from specific examples or evidence, making the conclusion probable but not certain.

Inductive arguments frequently use words like "most", "likely", or generalise based on observed cases. These arguments are fundamental for questions involving analogies, causality, and statistical claims.

Differences and LSAT Application

A clear distinction: deductive reasoning moves from the rule to the case; inductive reasoning moves from evidence to a rule or generalisation. LSAT Logical Reasoning tests both.

Key Term: premise
A statement presented as evidence or support for the argument’s conclusion.

Key Term: conclusion
The main claim or assertion the argument aims to establish as true using its premises.

Deductive vs. Inductive - Key Features Table

Worked Example 1.1

Argument: "Every contract entered freely is enforceable by law. David entered into a contract freely. Therefore, David’s contract is enforceable by law."

Answer:
This is a deductive argument. If both premises are true, the conclusion is certain. The reasoning is general to specific and relies on a universal principle.

Worked Example 1.2

Argument: "Out of 50 surveyed customers, 46 prefer online statements to paper. Thus, most customers likely prefer online statements."

Answer:
The argument uses inductive reasoning. It moves from specific survey results to a general (but not certain) conclusion about the wider population.

LSAT Question Stems and Reasoning

LSAT questions may not use the words "deductive" or "inductive", but they assess both types:

• Deductive question stems: "Which one of the following must be true?", "What can be properly inferred?"
• Inductive question stems: "Which conclusion is most strongly supported by the evidence?", "Which one of the following, if true, most strengthens the argument?"

Knowing which reasoning type the argument employs helps you choose the correct analytical method and avoid common errors.

Revision Tip

For deductive arguments, practice diagramming conditional statements and contrapositives. For inductive reasoning, check for representativeness and whether conclusions go beyond given evidence.

Common LSAT Mistakes

Exam Warning

Test-takers often misclassify inductive arguments as strongly valid (deductive). Always check if the evidence proves or only supports the conclusion. Don't assume a generalisation is a guarantee.

Summary

The LSAT Logical Reasoning section features both deductive and inductive arguments. Deductive reasoning leads to certain conclusions when rules are correctly applied; inductive reasoning supports probable conclusions based on observed evidence. Recognising which is present enables you to apply the right approach to must-be-true, inference, strengthening, weakening, analogy, and causal questions.

Key Point Checklist

This article has covered the following key knowledge points:

• Deductive reasoning leads to conclusions that must be true if premises are true; moves from general rules to specifics
• Inductive reasoning uses evidence or examples to suggest conclusions that are likely (but not certain); moves from specifics to generalisation
• LSAT Logical Reasoning questions may test both reasoning types, with question stems and argument structure giving clues
• Recognising the correct reasoning path is essential for valid LSAT answer choice elimination and correct response selection

Key Terms and Concepts

• deductive reasoning
• inductive reasoning
• premise
• conclusion