top of page
Search

What Is the Logical Opposite of "All", "Most" and "Some"? A Guide to Understanding Logical Negations

Writer's picture: Keonhee ChoKeonhee Cho

Updated: 4 days ago

If you're studying for the LSAT or diving into logical reasoning, you’ve likely encountered statements like "All cats are mammals" and wondered what the logical opposite of words like "all", "most" and "some" are. Understanding this concept is crucial for mastering the Logical Reasoning portion of the LSAT. For example, many people understand the importance of the Negation Technique in Necessary Assumption questions, but unfortunately many prep companies do not explain exactly how to negate. In this post, we’ll break down the logical opposite of "all," explain why it matters, and provide examples to help you apply this knowledge effectively.


What Is the Logical Opposite of "All"?

A logical opposite, also known as a negation, is a statement that would cover all other possibilities allowed by the original statement. This should not be confused with a polar opposite. A polar opposite is describing only the other extreme, whereas negations are encompassing all of the other possibilities. The LSAT is primarily concerned with logical opposites, not polar opposites. For example:

  • The logical opposite of "hot" is "not hot". "Cold" is not the proper negation because it is not the only other possibility (it could also be warm).


In logic, the word "all" is an absolute quantifier, meaning it makes a claim about every member of a group. For example, the statement "All birds can fly" asserts that every bird has the ability to fly.


Many LSAT students mistakenly believe the negation of this statement would be "All birds cannot fly" but notice how that does not encompass all the other possibilities. Even if just one bird is unable to fly, that would be enough to destroy the original claim. For this reason, the logical opposite of "all" is "not all" or "some are not." This means that at least one member of the group does not satisfy the condition. For instance:

  • Original Statement: "All birds can fly."

  • Logical Opposite: "Not all birds can fly" or "Some birds cannot fly."

This negation is essential because it directly challenges the universality of the original claim.



What Is the Logical Opposite of "Most"?

On the LSAT, "most" means "greater than 50%". A statement that would cover all possibilities outside of this range would cover possibilities ranging from 0% to 50%. Therefore, the negation of "most" is "not most". For example:

  • Original Statement: "Most birds can fly."

  • Logical Opposite: "Not most birds can fly" or "Less than most birds can fly"


What Is the Logical Opposite of "Some"?

On the LSAT, "some" means "greater than 0%". That means any number up to and including 100% can qualify as "some". The only possibility outside of that is 0%, so the negation of "some" is "none".

  • Original Statement: "Some birds can fly"

  • Logical Opposite: "No birds can fly" or "All birds cannot fly"



Why Understanding Logical Opposites Matters

  1. LSAT Logical Reasoning: Many LSAT questions require you to identify the logical opposite of statements, especially in Must Be True, Flaw, Necessary Assumption and Weaken questions. Knowing how to negate "all", "most", and "some" statements helps you eliminate incorrect answer choices and identify the correct one.

  2. Critical Thinking: Understanding logical opposites sharpens your ability to analyze LSAT arguments and identify weaknesses. For example, an author's conclusion could say something like "It is not true that all spiders are dangerous". Stating something is untrue is the same as stating that the negation is true. In situations like this, understanding the negation can help you have a clearer understanding of the conclusion, which is vital for understanding LSAT argumentation.


Examples of Logical Opposites in Action

Let’s look at a few additional examples to solidify your understanding:

  1. Example 1:

    • Original Statement: "All students passed the exam."

    • Logical Opposite: "Not all students passed the exam" or "Some students did not pass the exam."

  2. Example 2:

    • Original Statement: "All politicians are honest."

    • Logical Opposite: "Not all politicians are honest" or "Some politicians are not honest."

  3. Example 3:

    • Original Statement: "All successful candidates have strong analytical skills."

    • Logical Opposite: "Not all successful candidates have strong analytical skills" or "Some successful candidates lack strong analytical skills."



Conclusion

Understanding the logical opposites of "all", "most", and "some" are fundamental skills for LSAT logical reasoning and critical thinking. By mastering this concept, you’ll be better equipped to analyze arguments, identify flaws, and tackle challenging LSAT questions. Remember, the opposite of "all" is "not all"—not "none."


I hope you found this post helpful. Subscribe for more blog posts 

Check out my LSAT book on how to study and/or LSAT private tutoring -- I offer a free 2 hour trial session.

26 views0 comments

Recent Posts

See All

When Should You Take the LSAT?

Deciding when to take the LSAT is one of the most critical steps in your law school application journey. The timing of your test can...

Comments


bottom of page