Valid vs. Sound Arguments
(Why being logical isn’t always enough)
Arguments often sound convincing for one of two reasons:
either they follow a logical structure, or they align with something we already believe. Unfortunately, neither of those guarantees that the argument is actually any good.
To evaluate arguments properly, it helps to understand the difference between valid and sound reasoning.
What Is a Valid Argument?
An argument is valid if its conclusion follows logically from its premises.
That’s it.
Validity says nothing about whether the premises are true. It only asks a structural question:
If the premises were true, would the conclusion have to be true as well?
Example of a valid argument
All cats are reptiles.
Garfield is a cat.
Therefore, Garfield is a reptile.
This argument is valid, because the conclusion follows logically from the premises.
It is also obviously wrong — but not because of its structure.
What Is a Sound Argument?
An argument is sound if:
- It is valid, and
- Its premises are actually true
Soundness is stricter than validity. It requires both correct structure and accurate premises.
Example of a sound argument
All humans are mortal.
Socrates is human.
Therefore, Socrates is mortal.
This argument is both valid in form and true in content. The conclusion is justified.
Why the Difference Matters
Many bad arguments succeed by getting halfway there.
- Some arguments are valid but unsound
(the logic works, but the premises are false) - Some arguments are sound-looking but invalid
(the premises seem reasonable, but the conclusion doesn’t actually follow)
Understanding this distinction helps prevent a common mistake:
confusing logical form with truth.
An argument can be perfectly logical and still be wrong.
Where People Go Wrong
Common failures include:
- Assuming a conclusion is true because the reasoning “felt logical”
- Treating validity as proof that the premises are correct
- Ignoring structure entirely and focusing only on whether the conclusion is appealing
This is why fallacies like Affirming the Consequent are so persuasive: they often imitate valid forms while quietly breaking the rules.
A Useful Habit
When evaluating an argument, ask two separate questions:
- Does the conclusion follow from the premises?
(Validity) - Are the premises actually true?
(Soundness)
If the answer to either is “no,” the argument fails.
Why Skeptics Care
Skepticism isn’t about rejecting claims reflexively. It’s about holding conclusions to appropriate standards. Understanding valid vs. sound arguments helps ensure that reasoning is doing the work — not confidence, repetition, or intuition.
Being logical is good.
Being right for the right reasons is better.