Validity
Good arguments are very persuasive and can convince people to accept the point that you re trying to make. These types of good arguments can be described was reliable arguments.
In critical thinking the definition for reliable arguments is very precise. The first part of a reliable argument is good structure. If an argument is not well structured then it is not a reliable argument.
An argument with a good structure is called a valid argument. An argument with bad structure is called invalid.
A valid argument is one that forces you to accept the conclusion if you can accept its premises. Look at the example below...
Example
P1 - All monkeys are mammals.
P2 -Charlie is a monkey.
C - Charlie is a mammal.
If we accept that all monkeys are mammals and that Charlie is a monkey then we have to accept that Charlie is a mammal.
If we didn't accept that Charlie is a mammal then we would be contradicting ourselves.
Valid Example
P1 - All men are humans.
P2 - Socrates is a man.
C - Therefore, Socrates is a human.
Invalid Example
P1 - All men are humans.
P2 - Socrates is human.
C - Therefore Socrates is a man.
Can you tell why the second example is invalid?
The second argument assumes that because Socrates is human that he therefore must be a man but that is not necessarily the case.
What if the Socrates in the second argument is actually a woman?
She would still be a human but would not be a man.
Remember, a valid argument is one which compels us to accept the conclusion if we accept the premises.
We can accept that all men are humans and that Socrates is human, but we can't accept that he or she is a man.
This is why the argument is invalid.
Another way to explain validity is to say that a valid argument is one where the conclusion logically follows from the premise
Some arguments are obviously invalid, like the one below on the right. The Socrates example however is much harder to spot as invalid. This is why it is important to study arguments in philosophy.
Valid Example
P1 - All Frenchmen are French
P2 - Descartes is a Frenchman.
C - Therefore, Descartes is French.
Valid Example
P1 - No dogs are bus drivers.
P2 - Fido is a dog.
C - Therefore, Fido is not a bus driver.
Invalid Example
P1 - All French men are French.
P2 - Descartes is a Frenchman.
C - Therefore, Charlie is a monkey.
Invalid Example
P1 - No dogs are bus drivers.
P2 - Bob isn't a dog.
C - Therefore, Bob is a bus driver.
Tips
A valid argument is an argument which guarantees a true conclusion if the the premises are true.
If you see an argument with true premises and a false conclusion then you know straight away that it is invalid.
Tasks
Let's practice identifying valid and invalid arguments.
Complete the following tasks.
Read through the instructions as they will be a bit different for each task.
There are copies on your GoogleClassroom too.