CRITICAL THINKING - Fundamentals: Validity [HD]

In this Wireless Philosophy video, Paul Henne (Duke University) discusses the philosophical concept of validity. After reviewing the structure of an argument, he defines validity: an argument is valid if and only if its premises guarantee the conclusion. He reviews a few examples of validity and invalidity, and he leaves you with one example to figure out on your own.

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[alcatraz]

shout out to all my fellow university students trying to get by in there philosophy course

[jamieg]

If you want to think more abstractly about these types of problems without having to replace things with letters or choose new items that make the premises true, here's an interesting approach that thinks of the items as boxes being placed into other boxes. This works because putting things in boxes allows us to imagine items in physical positions, making their relationships to each other in space clear.

*Original*
All fruit is a chair.
Square is a chair.
Conclusion: Square is a fruit.

*Box Translation*
The fruit box is in the chair box.
The square is in the chair box.
Conclusion: Is the square in the fruit box?

Answer: No, as far as we know, we only put the square in the chair box.

Premises tell you to take an item and put it in a box. Conclusions are yes or no questions about which box an item is in.

For a comparison, look at this valid version of the argument:

*Valid version*
All fruit is a chair.
Square is a fruit.
Conclusion: Square is a chair.

*Box Translation*
The fruit box is in the chair box.
The square is in the fruit box.
Conclusion: Is the square also in the chair box?


Answer: Yes, since the square is in the fruit box and the fruit box is in the chair box, the square has to also be in the chair box.

[kierafernandes]

this is so hard!!! i have to know this for class and once i start feeling like i finally understand i get hit with a question and everything i thought i knew goes out the trash.

[jordansmith]

Invalid. All fruit may be a chair, but vegetable may be a chair as well. Square could be vegetable.

[Uncivil-Engie]

The last argument is invalid. Truth of C1 doesn't necessarily follow from the truth of both P1 and P2 (for example if both fruit and chair were both non-overlapping subsets of chair). However changing the second premise to "A square is a fruit" would make this into a valid argument.

[Matt-nogg]

It becomes borderline impossible for me to understand what's going on when they throw out nonsense phrases like "all fruit is a chair"

[amandajane]

Had an assignment for my ethics class and this helped so much. I was struggling for an hour until I found this video. Thank you!

[sznio]

invalid because all fruit may be chairs, but not all chairs might be fruit.

if you say "Square is a fruit" and "Therefore, Square is a chair", that would be valid.

[VOLightPortal]

Valid:
A is B (coffee is a bean)
B is C (bean is a food)
Therefore A is C (coffee is a food)
Invalid:
A has B (dogs have fur)
C has B (Claire has fur)
Therefore C is A (Claire is a dog)

[PringlesOriginal]

Thankyou, I feel a lot clearer on this however I still feel like I haven't fully grasped the concept of validity in philosophy.

[spammeplenty]

Invalid. It's easier to see with term substitution where the premises are accepted to be true:
All Lamborghini Countachs are cars.
A Honda Civic is a car.
Therefore, a Honda Civic is a Lamborghini Countach.

All citrus fruits are acidic.
An orange is acidic.
Therefore, an orange is a citrus fruit.

All architects are people.
A landlord is a person.
Therefore, a landlord is an architect.

All three examples follow the same form of argument, but one example arrives at a false conclusion, one a true conclusion, and the last at a contingient conclusion. In an invalid argument, the truth of the premises does not *guarantee* the truth of the conclusion. As it so happens, inductive arguments, the mainstay of science, are invalid arguments.

[happyarmadillofarm]

Correct me if I'm wrong and you might have to draw this out... In a Venn Diagram the large rectangle would be labeled chair. Within the large rectangle would be a circle named fruit since "all fruit is a chair". Then the X mark representing square would be on the border of the circle named fruit due to the second statement not saying explicitly if square is or isn't a fruit. So there's a possibility that square is something other than a fruit making the argument invalid.

[TurteXing]

In programming we use something similar to this called inheritance. Saying all Fruit is a Chair is like saying Fruit is a child of chair. This relationship is one way, Chair could have multiple children but Fruit can only have one parent. Therefore if Square is a Chair then it could be a Fruit. If Square was defined as a Fruit then it must also be a Chair.

[jacobmartin]

This makes sense intuitively, but I'm interested to know more about exactly how an argument is determined to be valid. What is the method for determining if an inference follows from the premises?

[trilobyte]

what the heck? he didn't give the answer at the end of the video!

[phantomfrk]

I was a mathematics major and for some reason this confused the heck out of me.  Not sure if it was because I have a background in logic or just the way it was explained?

[rac]

What about this argument:
P1: LA county requires a vaccine mandate to enter stores.
P2: Vaccine mandates are discriminatory
C: Therefore, LA county is discriminatory.

[nathanfoss]

They could have explained the concept much better.
I will try to summarize the video in simple terms.

1) An argument is a list of statements that support a conclusion or answer a question.
2) A statement, in an argument, is known as a premise.
3) A valid argument is an argument in which all of the premises agree with each other, assuming that the premises are true. In other words, it’s valid when the premises do not conflict nor contradict the each other and we say the premises are true.
4) A valid argument does not identify if the argument is true or false, rather a valid argument only identifies if the premises support the conclusion or not.

Example 1:
P1: Bobby eats all foods that are red.
P2: Bananas are red.
Conclusion: Bobby eats bananas.

In Example 1, the argument is valid but not true because P2 is not true, yet all of the premises agree if we assume P2 is true.

Example 2:
Question: Is the world round?
P1: Bobby says the world is flat.
P2: Bobby is always right.
P3: The world has been proven to be round.
Answer: Yes, the world is round.

In Example 2, the argument is not valid yet true because the world is round but the premises don’t agree.

We can use valid arguments to find the best answer when our known information is incorrect or limited. We can then find better answers to our questions using another valid argument as we learn the correct or new information.
That’s why we should be humble and unbothered when someone criticizes our ideas and actions. What you think you know might be valid but not correct nor true.

Great video thank you!

[gimarsonpal-oy]

Im trynna getting this philosophy course so that i can enhance my arguments skills, that can be necessarily used in law school.

[TheDavid]

"Metaphysics As A Guide to Morals" by Iris Murdoch is a must read!