Common logical fallacies and reasoning errors - Equivocation...

Learning Outcomes

By the end of this article, you will be able to identify and explain the reasoning errors of equivocation and ambiguity in LSAT arguments. You will understand how subtle shifts in language can weaken or invalidate reasoning, recognise the forms such fallacies can take, and apply effective strategies to avoid being misled by ambiguous or equivocal argumentation in assessment scenarios and LSAT questions.

LSAT Syllabus

For LSAT, you are required to understand logical reasoning fallacies, including equivocation and ambiguity. In revision, focus on:

• recognising when an argument conflates two different meanings of the same term (equivocation)
• identifying arguments that use unclear or ambiguous language to obscure reasoning or lead to invalid inferences
• distinguishing fallacies of language from other kinds of argument flaws in question stems and answer choices
• eliminating answer choices that exploit shifts in language to mimic validity

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 the following is an example of equivocation?
   1. The word “bank” is used first to mean “riverbank,” then to mean “financial institution.”
   2. An argument appeals to an authority irrelevant to the subject.
   3. The argument compares the past with the present.
   4. The argument assumes something is true for all members of a group because it’s true for one member.
2. Which statement best describes the ambiguity fallacy?
   1. The premises rely on a single, clear definition of each term.
   2. The argument contains a word or phrase open to multiple interpretations, making the conclusion unclear.
   3. The argument draws a strong causal link between two unrelated events.
   4. The reasoning is circular, restating the conclusion.

3. True or false? A shift in the meaning of a word within an argument always invalidates the reasoning.

Introduction

Equivocation and ambiguity are two common language-based fallacies assessed in LSAT logical reasoning. These errors occur when arguments use words or phrases unclearly—either by switching meanings, using inherently vague terms, or failing to clarify context. Detecting these flaws is essential for interpreting arguments accurately and choosing the correct answer in flaw or assumption questions.

Key Term: equivocation
The logical flaw in which an argument uses a key word or phrase in more than one sense, usually shifting its meaning partway through the reasoning.

Key Term: ambiguity
The use of a word, phrase, or sentence which is open to two or more plausible interpretations, resulting in unclear or unreliable reasoning.

Equivocation: Shifting Meanings

Equivocation arises when an argument covertly changes the definition of a word or phrase between the premises and the conclusion. This shift allows the appearance of a valid connection where none exists.

Key Term: fallacy of equivocation
A logical flaw where the difference in meaning is concealed, so the argument relies on an unstated switch in interpretation.

Worked Example 1.1

Argument: "A feather is light. What is light cannot be dark. Therefore, a feather cannot be dark."

Answer:
This argument equivocates on the word "light." In the premise, "light" means "not heavy." In the conclusion, "light" means "not dark in colour." The argument is logically invalid because it uses two different meanings.

Typical Question Stem Cues

• “The argument’s reasoning is flawed because it relies on a key term with two different meanings.”
• “Which one of the following describes a problem in the way the argument uses language?”

Ambiguity: Vagueness and Unclear Meaning

Ambiguity occurs when an argument uses a word, phrase, or structure that is unclear or could have more than one interpretation. The argument then draws a conclusion as if only one (convenient) meaning applies.

Worked Example 1.2

Argument: "Children’s drawings are hard to bear. Therefore, teachers should not have to bear them."

Answer:
The term “hard to bear” is ambiguous—does it mean “difficult to see” (quality), or “heavy to carry”? The argument exploits this ambiguity to draw an unsupported conclusion.

Revision Tip

When evaluating for ambiguity, always ask: Could any term, phrase, or example reasonably be understood in more than one way? If yes, the argument may lack clarity.

Detection and Elimination Strategies

Step 1: Identify Key Words

Underline terms central to the argument’s logic, especially if the meaning could shift or if the word has multiple definitions.

Step 2: Compare Uses

Check whether the meaning of the word changes or is unclear between premises and conclusion. If so, consider an equivocation or ambiguity fallacy is present.

Step 3: Check Question Stems

LSAT items often reference “shifts in meaning,” “ambiguous” language, “unclear references,” or “problematic use of a term.” Select these as possible flaw descriptors if you see equivocation or ambiguity in the passage.

Exam Warning

Many LSAT distractors use tempting but ambiguous terms or mimic language from the argument. Eliminate answer choices that depend on broad, vague, or double-meaning words with unclarified context.

Why Equivocation and Ambiguity Matter on the LSAT

Language-based fallacies allow arguments to appear valid by hiding unclear or shifting terms. The LSAT frequently tests your ability to spot these reasoning flaws, especially in flaw, parallel reasoning, or method of reasoning questions. They are rarely the correct answer to a strengthen/weaken or assumption question (unless the ambiguity is resolved or clarified).

Worked Example 1.3

Argument: "Laws can be changed by people. What can be changed by people can be ignored by people. Therefore, laws can be ignored by people."

Answer:
The first use of "can be changed by people" means "subject to amendment," while the second implies "not necessary to follow." This is a fallacy of equivocation: shifting sense of "can be changed" to justify ignoring laws.

Key Point Checklist

This article has covered the following key knowledge points:

• Arguments may exploit either a shift in the meaning of a term (equivocation) or the unclear use of language (ambiguity)
• Equivocation occurs when a key term is used with more than one meaning in an argument
• Ambiguity occurs when a word or phrase is open to several meanings, undermining the validity of the conclusion
• On LSAT, always clarify the meaning of critical terms before accepting an argument’s reasoning as valid
• Eliminate answer choices that rely on broad, vague, or double-meaning words left undefined in the argument

Key Terms and Concepts

• equivocation
• ambiguity
• fallacy of equivocation