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Evaluating arguments and recognize valid reasoning is a key skill in critical thinking—and once you master it, you’ll be able to spot weak arguments and build stronger ones of your own.
Step 1: Spotting Flaws in Reasoning
When you evaluate an argument, your goal is to find any flaws or weaknesses in the reasoning. Ask yourself:
Step 1: Spotting Flaws in Reasoning
When you evaluate an argument, your goal is to find any flaws or weaknesses in the reasoning. Ask yourself:
How big is the flaw?
Does it affect the entire argument or just one part?How serious is it?
Does it completely destroy the claim, or just make it less convincing?Is anything still salvageable?
Even if part of the argument is flawed, could a weaker version still make sense?
Step 2: Understanding Validity
Step 2: Understanding Validity
Validity is all about the structure of an argument—not whether the statements are true, but whether the reasoning is logically sound.
A valid argument means: If the reasons are true, then the conclusion must also be true.
Think of it like math or coding: the logic has to follow a clear pattern.
Step 3: Using Letters to Represent Logic
Step 3: Using Letters to Represent Logic
To focus on structure, we often use letters like p and q:
If p, then q.
p is true.
Therefore, q is true.
This is called Modus Ponens—a valid form of reasoning.
Examples of Valid Arguments:
Examples of Valid Arguments:
If Emma is a student at Sunny Coast College, she can borrow books.
Emma is a student.
So, she can borrow books.
If a compound is acidic, it turns litmus paper red.
This compound is acidic.
So, it turns the paper red.
Even if the content is silly, the structure can still be valid:
If someone is 3 meters tall, they can touch the moon.
My friend is 3 meters tall.
So, they can touch the moon.
(Valid structure, but obviously false in reality!)
Step 4: The Negative Version
Step 4: The Negative Version
Another valid structure flips the logic:
If p, then q.
q is not true.
Therefore, p is not true.
Examples:
Examples:
If Emma is a student, she can borrow books.
She can’t borrow books.
So, she’s not a student.
If a compound is acidic, it turns litmus paper red.
It doesn’t turn red.
So, it’s not acidic.
Step 5: Watch Out for Invalid Structures
Step 5: Watch Out for Invalid Structures
Some arguments look logical but are actually flawed. These are invalid:
If p, then q.
q is true.
So, p is true. ❌If p, then q.
p is false.
So, q is false. ❌
Examples of Invalid Arguments:
Examples of Invalid Arguments:
If Sofia is a student, she can borrow books.
She can borrow books.
So, she must be a student
(Maybe she’s a teacher or a guest member!)
If Petra is a student, she can borrow books.
She’s not a student.
So, she can’t borrow books.
(Again, she might qualify in another way.)
Necessary and Sufficient Conditions
A necessary condition is something that must be true or must happen for something else to be true or happen.
Example:
Example:
To get into a movie theater, you must have a ticket.
Having a ticket is necessary to enter.
But just having a ticket doesn’t guarantee you’ll see the movie—you might be late, or the theater might be closed. So it’s necessary, but not always enough.
A sufficient condition is something that, if it happens, guarantees that something else will happen.
Think of it like a guarantee.
Example:
Example:
If you score 100% on the test, you will pass the course.
Scoring 100% is sufficient to pass.
But it’s not necessary—you could also pass with 85%. So scoring 100% is more than enough, but not the only way.
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