Logical reasoning question types - Complete the argument (fi...

Learning Outcomes

After reading this article, you will be able to: identify and analyze LSAT "Complete the argument" (fill-in-the-blank) Logical Reasoning questions; determine what premises and conclusions are needed to make an argument logically complete; evaluate answer choices using careful process of elimination; and avoid common missteps found on these question types. You will be ready to efficiently solve argument completion prompts on the real LSAT.

LSAT Syllabus

For LSAT, you are required to understand how 'Complete the argument' (fill-in-the-blank) question types operate within Logical Reasoning. In your revision, make sure you are familiar with:

• Identification and structure of fill-in-the-blank argument prompts
• How to analyze the logical gap and determine what is missing in the argument
• Techniques for evaluating which answer most validly completes the argument’s reasoning
• Typical logical patterns and common distractor options in completion questions

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. In a 'Complete the argument' LSAT question, what is typically missing from the stimulus?
   1. A premise
   2. A conclusion
   3. Either a premise or conclusion
   4. Cannot be determined
2. Which approach is generally most effective when tackling these prompts?
   1. Plugging each answer into the blank and reading for fit
   2. Looking for word-for-word matches from the passage
   3. Picking the most positive statement
   4. Choosing the answer that is the longest

3. True or false? The correct choice must both be supported by and support the rest of the argument.

4. True or false? In these questions, the blank is always at the end of the stimulus.

Introduction

LSAT Logical Reasoning questions that ask you to 'complete the argument' present a stimulus with a blank line, usually at the conclusion or sometimes within the premises. Your task is to select the answer choice that best fills the gap so the argument's structure is logically valid or the argument is most strongly supported.

Key Term: complete the argument (fill-in-the-blank) question
An LSAT Logical Reasoning prompt where you must select the answer choice that best completes the argument, given a blank in the stimulus.

The Structure of Fill-in-the-Blank Prompts

Fill-in-the-blank questions mimic the structure of other Logical Reasoning argument types but replace a key inference, premise, or conclusion with a blank (__). The blank may be at the end of the stimulus (most common, for the conclusion), but may sometimes be embedded earlier (as an assumption or intermediate step).

Most question stems ask which option "most logically completes the argument" or "most appropriately fills in the blank".

Key Term: logical gap
The missing step—either premise, assumption, or conclusion—that must be supplied for the argument to be logically complete.

Step-by-Step Approach

To answer these questions efficiently:

1. Read the question stem to determine if you must supply a premise, conclusion, or assumption.
2. Analyze the argument before the blank: Identify the structure—what is stated, and what is missing?
3. Predict, in your own words, what is needed to make the argument’s logic flow.
4. Plug each answer into the blank and check which provides the strongest, most logical completion.
5. Use process of elimination to dismiss answers that are too strong, too weak, irrelevant, or out of scope.

Worked Example 1.1

A stimulus says:

"All successful startups adjust rapidly to technology changes. NanoTech's leadership has consistently invested in tech upgrades. Therefore, __"

Which answer most logically completes the argument?

A) NanoTech adjusts rapidly to technology changes
B) All startups are successful
C) NanoTech is a successful startup
D) Investing in upgrades guarantees success
E) Successful startups always invest in upgrades

Answer:
Choice A is correct. The premises suggest NanoTech adjusts rapidly. Choice C is too strong because the argument does not guarantee success, only that flexibility in response to change is a trait of success.

Typical Locations of the Blank

While the blank is usually the main conclusion at the end, sometimes it may ask you to fill in a missing premise or necessary inference. Read carefully: "The argument above is most strongly supported by which one of the following?" indicates you are looking for a conclusion, while "the reasoning above most depends on which of the following..." may require an unstated assumption.

Key Term: premise
A statement that provides evidence or support for the argument's conclusion.

Identifying What Is Needed

After identifying if the blank requires a premise or conclusion:

• If the missing piece is a conclusion, the correct answer must integrate all available premises and flow logically from them.
• If the missing piece is a premise or assumption, the correct answer must logically support the conclusion, bridging premises to the end point.
• The correct answer must not contradict any stated parts of the stimulus.

Worked Example 1.2

Stimulus:

"In recent years, more energy-efficient cars have come to dominate the market. Sales data show that green vehicles outsell non-efficient models. Therefore, it is likely that __"

A) Drivers prefer fuel-efficient cars
B) Non-efficient models will always be available
C) Fuel-efficient car sales will decrease
D) Most green vehicles are inexpensive
E) The government should subsidize green cars

Answer:
Choice A is correct. This conclusion matches what is supported by the stimulus; the remaining answers are unsupported or out of scope.

Evaluating the Answer Choices

• Insert each answer into the blank, reading the argument as a whole.
• Eliminate answers that do not logically follow from, or support, the argument.
• Be alert for answer choices that introduce extreme language or ideas not present in the stimulus.
• Discard options that are out-of-scope, reverse the logic, or simply repeat a premise.

Revision Tip

For these prompts, always try to paraphrase what logically belongs in the blank before reviewing the answer choices.

Common Distractor Types

Typical traps in these questions include:

• Restating a premise without completing the argument
• Going beyond the argument, introducing stronger claims than the premises support
• Stating something unrelated or too general
• Using language that is too absolute (e.g., "all," "only," "never") without justification

Worked Example 1.3

Stimulus:

"Every time the city increases bus fares, ridership declines. This year, fares are set to increase. Therefore, we can expect __"

A) Increased revenue from higher fares
B) Fare increases will cause the city’s economy to collapse
C) A decline in ridership
D) All city residents oppose fare increases
E) No effect on public transport use

Answer:
C. The prior pattern supports expecting a decline in ridership following a fare increase.

Exam Warning

Do not assume the blank always requires a conclusion. Some questions want you to supply a conditional, premise, or assumption; check the question stem carefully.

Summary

Key Point Checklist

This article has covered the following key knowledge points:

• Fill-in-the-blank questions require completion of a logical argument using a premise, conclusion, or assumption
• The blank is most often the conclusion but may sometimes be a premise or assumption—always read the question stem carefully
• Successful strategy: Predict what is logically needed before reading choices, then plug in each answer and eliminate incorrect ones
• Typical wrong answers include mere premise restatements, out-of-scope claims, and overly strong or weak conclusions
• Watch for extreme language not supported by the argument

Key Terms and Concepts

• complete the argument (fill-in-the-blank) question
• logical gap
• premise