Lost on Valid and Invalid Argument forms

tringo335

I am having a hard time understanding this section of the lesson and am hoping some folks can weigh in on it. I think I'm a bit lost because there is little context on when I would be using these tools and how. Also, I am unsure exactly what to memorize. Should I be memorizing both the valid and invalid diagrams and be prepared to use them in future lessons? Also could someone explain exactly which types of questions these will be useful for? Thanks in advance.

Rigid Designator

As far as context goes, since validity and invalidity are logical properties to do with the structure of arguments, the concepts are (broadly speaking) going to be relevant whenever we're dealing with questions about argument structures.

In particular though the concepts will be employed in questions like Must Be True questions. Must Be True questions supply us with information, or premises, and ask us to decide what must be the case given that information. In other words, they're asking us to find the answer choice which, when paired with the premises in the stimulus, produce a valid argument. Thus validity is a useful tool we can use when tackling these sorts of questions.

As for what to memorize... (and this is just my 2 cents)... if you're comfortable with the definition of a valid argument (conclusion can't be false if all its premises are true) you don't need to memorise anything else in particular.

EDIT: I found this example from the CC which might be useful https://7sage.com/lesson/cigarette-smoke-stimulate-gene-mbt-question/

jknauf

We will be using valid argument forms for sufficient assumption and must be true questions. The reason we will be using valid argument forms on these specifically is because these questions must meet the standard of 100% logical validity given that we accept all the premises as true.

For a sufficient assumption question we'll be asked to to supply a missing piece of the argument. For example:

A --> B
A

===========
A --> C

What assumption is missing from this argument to make the conclusion follow logically?

Well, if we know our valid argument forms, we can recognize that in order to get to C we need the assumption B --> C. So lets plug that in an see what we get

A --> B --> C
A

===========
A --> C

Ahh ok now we have a perfectly valid argument.

For must be true questions, our objective is slightly different. We are given an argument or fact set and asked to determine what must be true on the basis of the information inside the stimulus.

A must be true questions could be something like this:

A --> B --> C - what can we infer that must be true from these premises?

===========

Inferences:

A --> C
A --Most--> B
A --Most--> C
A <-Some-> B
A <-Some-> C

And of course, our contrapositives:

/C --> /A
/B --> /A

There is a few more here, but this should give you a pretty good idea. All of these could be answers correct answers on a must be true question, so we must intuitively understand the logic. You will hear JY mention a few times in the CC that if you are looking to score a 170+, these questions must be 'freebies' or 'layups' if you will.

Best of luck!

BinghamtonDave

A valid argument is a construction of an argument that logically allows us to draw a specific conclusion. So if I tell you something like:
All cats are mammals and all mammals are endothermic, we are logically allowed to support the conclusion: all cats are endothermic. There are several ways to conceptualize these concepts: i.e. the "bucket method" referred to in the lessons etc. What is important with these forms is that we come away from the lessons with an intuitive and instinctual understanding of the abstract form of the arguments. In the above example, the abstract form would be: If A---->B----->C, known in the curriculum as valid argument form #3.
The LSAT calls upon this knowledge in a variety of different questions: from MBT to MBF to parallel reasoning to even sufficient assumption questions.

Taking just the example above and crafting it in a certain way, the exam could ask us for a sufficient assumption.
The premise could be: All cats are mammals, and the conclusion could be: therefore, all cats are endothermic. The sufficient assumption to make this argument valid would be: if something is a mammal then it is endothermic. The abstract form being we are given A--->B as a premise and on the basis of that premise we conclude A--->C. The missing link of course abstractly being B---->C. There are lessons and quizzes that go into greater depth on this topic within the curriculum.

*This being the LSAT, there are a variety of ways to obscure the way in which the phrase "All mammals are endothermic" is said structurally in English in an answer choice, to as Mr. Ping puts it in the lessons: "scale the difficulty of the question."

In summation, if I were to give someone 1 single piece of advice on their journey to getting a high score on this exam it would be to develop a deep understanding of the way arguments function through the study of valid argument forms and conditional logic. My advice would be straight forward: learn them, apply them during BR. The second piece of advice would be to develop a deep and instinctual understand of the way our language functions grammatically. Often times, an argument can be parsed out on the basis of grammatical indicators.

I hope this helps
David

PS: here is a test to know if you truly understand the valid argument forms intuitively: if when reading arguments on LR you can predict the way in which the argument is going before continuing onto the next sentence and you turn out to be correct: you are in command of that question and your skills are there. This is a huge part of how people can get LR sections done in 28-29 minutes.

Alex

Yes, I would memorize them. They are useful anywhere you encounter conditional logic on the test. However, more important than simply memorizing them is making sure you understand them.

Question types like Inference questions, S.A, and Parallel reasoning questions are much, much simpler when you know your valid and invalid argument forms. Before I learned the valid and invalid argument forms, my accuracy on parallel reasoning questions was probably 60%. I just couldn't visualize what a correct answer would look like. The valid/invalid argument forms were a game changer. It also helps with speed and confidence throughout the LR section.

tanes256

@tringo335 I didn't understand why I needed to understand or memorize the invalid argument forms so I skimmed through all of it initially. It wasn't until much later on that I realized that memorizing the invalid argument forms are just as helpful because if you have to plug in an AC somewhere you will quickly notice the invalid argument form, if applicable, and confidently eliminate that AC and move on, thus saving time.

Pink Dust

I memorized both valid and invalid forms but I found that it sort of confused me!
So I went back and just memorized the valid forms. If I see another form that isn't one of the forms I memorized (valid ones) I know it is invalid!
In terms of when to use it, I am slowly figuring out that when I see a SA question for example. that I don't just jump to trying to map it out into logic. First understand what it is saying to me, quickly glance the questions. Sometimes you don't need to map it into logic. And if you get fixated on oh I need to map this to do get this right, you could be wasting time because sometimes its really hard to map out in the first place! This is also the same for must be true questions.
I used to go into this robotic mode and try to map everything out on LR for questions like SA, MBT, Parallel but sometimes I can just do it without mapping it out and it saves me a lot of time.
Idk i feel like this exam comes together with practice -_-

tringo335

@"Pink Dust" said:
I memorized both valid and invalid forms but I found that it sort of confused me!
So I went back and just memorized the valid forms. If I see another form that isn't one of the forms I memorized (valid ones) I know it is invalid!
In terms of when to use it, I am slowly figuring out that when I see a SA question for example. that I don't just jump to trying to map it out into logic. First understand what it is saying to me, quickly glance the questions. Sometimes you don't need to map it into logic. And if you get fixated on oh I need to map this to do get this right, you could be wasting time because sometimes its really hard to map out in the first place! This is also the same for must be true questions.
I used to go into this robotic mode and try to map everything out on LR for questions like SA, MBT, Parallel but sometimes I can just do it without mapping it out and it saves me a lot of time.
Idk i feel like this exam comes together with practice -_-

I feel the same as you; after the valid section I felt somewhat in control of what I had just learned but when he launched into invalid I was lost again. I too thought of just memorizing the valid and when I saw one I didn't recognize, I knew it would be invalid. @BinghamtonDave @"Alex Divine" @jknauf @tanes256 do you think this method would work?

tringo335

@jknauf said:
We will be using valid argument forms for sufficient assumption and must be true questions. The reason we will be using valid argument forms on these specifically is because these questions must meet the standard of 100% logical validity given that we accept all the premises as true.

For a sufficient assumption question we'll be asked to to supply a missing piece of the argument. For example:

A --> B
A

===========
A --> C

What assumption is missing from this argument to make the conclusion follow logically?

Well, if we know our valid argument forms, we can recognize that in order to get to C we need the assumption B --> C. So lets plug that in an see what we get

A --> B --> C
A

===========
A --> C

Ahh ok now we have a perfectly valid argument.

For must be true questions, our objective is slightly different. We are given an argument or fact set and asked to determine what must be true on the basis of the information inside the stimulus.

A must be true questions could be something like this:

A --> B --> C - what can we infer that must be true from these premises?

===========

Inferences:

A --> C
A --Most--> B
A --Most--> C
A <-Some-> B
A <-Some-> C

And of course, our contrapositives:

/C --> /A
/B --> /A

There is a few more here, but this should give you a pretty good idea. All of these could be answers correct answers on a must be true question, so we must intuitively understand the logic. You will hear JY mention a few times in the CC that if you are looking to score a 170+, these questions must be 'freebies' or 'layups' if you will.

Best of luck!

Thank you! This helps a lot; I remember JY saying in order to get 170+, you'll have to know this in and out so I intend on getting this down before moving on

tringo335

@BinghamtonDave said:
A valid argument is a construction of an argument that logically allows us to draw a specific conclusion. So if I tell you something like:
All cats are mammals and all mammals are endothermic, we are logically allowed to support the conclusion: all cats are endothermic. There are several ways to conceptualize these concepts: i.e. the "bucket method" referred to in the lessons etc. What is important with these forms is that we come away from the lessons with an intuitive and instinctual understanding of the abstract form of the arguments. In the above example, the abstract form would be: If A---->B----->C, known in the curriculum as valid argument form #3.
The LSAT calls upon this knowledge in a variety of different questions: from MBT to MBF to parallel reasoning to even sufficient assumption questions.

Taking just the example above and crafting it in a certain way, the exam could ask us for a sufficient assumption.
The premise could be: All cats are mammals, and the conclusion could be: therefore, all cats are endothermic. The sufficient assumption to make this argument valid would be: if something is a mammal then it is endothermic. The abstract form being we are given A--->B as a premise and on the basis of that premise we conclude A--->C. The missing link of course abstractly being B---->C. There are lessons and quizzes that go into greater depth on this topic within the curriculum.

*This being the LSAT, there are a variety of ways to obscure the way in which the phrase "All mammals are endothermic" is said structurally in English in an answer choice, to as Mr. Ping puts it in the lessons: "scale the difficulty of the question."

In summation, if I were to give someone 1 single piece of advice on their journey to getting a high score on this exam it would be to develop a deep understanding of the way arguments function through the study of valid argument forms and conditional logic. My advice would be straight forward: learn them, apply them during BR. The second piece of advice would be to develop a deep and instinctual understand of the way our language functions grammatically. Often times, an argument can be parsed out on the basis of grammatical indicators.

I hope this helps
David

PS: here is a test to know if you truly understand the valid argument forms intuitively: if when reading arguments on LR you can predict the way in which the argument is going before continuing onto the next sentence and you turn out to be correct: you are in command of that question and your skills are there. This is a huge part of how people can get LR sections done in 28-29 minutes.

This gives me so much context; thank you!!! In later lessons will JY be showing how to apply validation to specific questions?

jknauf

@tringo335 said:

I feel the same as you; after the valid section I felt somewhat in control of what I had just learned but when he launched into invalid I was lost again. I too thought of just memorizing the valid and when I saw one I didn't recognize, I knew it would be invalid. @BinghamtonDave @"Alex Divine" @jknauf @tanes256 do you think this method would work?

Well, memorizing will work for the short term. But you need to work on internalizing the logic. At the beginning, your understanding will be "Ok I know A->B->C therefore A->C is a valid argument form, because JY has told me so"

But to obtain mastery you need to understand WHY

A-->B some C doesnt give us A some C.

Also you need to understand WHY

A some B --> C gives us A some C

If you just use memory, you could be stuck in a situation under timed where you are frantically trying to recall from memory the valid argument forms. Instead of intuitively working through the problem the most efficient way.

These are the fundamentals which you must internalize if you want a high score in the LR section. The LSAT authors will get nasty with their logical chains. And when they do, we do not want to be relying on memory, but rather understanding and intuition. For example, a sufficient assumption problem I worked on the other day was as follows

/F some SA ---M--> VCP ---> GAR

Conclusion: GAR some F

Well damn, how do we get the conclusion to follow from here?

We first have to make an inference SA ---M--> VCP ---> GAR gives us the inference SA ---M--> GAR. So from here, if we add the assumption
SA --M--> F

We are left with this

SA ---M--> GAR

SA ---M--> F

Conclusion: GAR some F

SA--M--> F was the sufficient assumption needed to conclude GAR some F

Valid argument 9 https://7sage.com/lesson/valid-argument-form-9-of-9/

You need to be able to work through these intuitively which will come with time, as long as you don't just settle with memorization.

tringo335

@jknauf said:

@tringo335 said:

I feel the same as you; after the valid section I felt somewhat in control of what I had just learned but when he launched into invalid I was lost again. I too thought of just memorizing the valid and when I saw one I didn't recognize, I knew it would be invalid. @BinghamtonDave @"Alex Divine" @jknauf @tanes256 do you think this method would work?

Well, I think memorizing will work for the short term. But you need to work on internalizing the logic. At the beginning, your understanding will be "Ok I know A->B->C therefore A->C is a valid argument form, and same with the 8 other valid argument forms"

But to obtain mastery you need to understand WHY A-->B some C doesnt give us A some C. Also you need to understand WHY A some B --> C gives us A some C. If you just use memory, you could be stuck in a situation under timed where you are frantically trying to recall from memory the valid argument forms. Instead of intuitively working through the problem the most efficient way.

These are the fundamentals which you must internalize if you want a high score in the LR section. The LSAT authors will get nasty with their logical chains. For example, a sufficient assumption problem I work one the other day was as follows

/F some SA ---M--> VCP ---> GAR

Conclusion: GAR some F

Well damn, how do we get the conclusion to follow from here?

We first have to make an inference SA ---M--> VCP ---> GAR gives us the inference SA ---M--> GAR. So from here, if we add the assumption
SA --M--> F

We are left with this

SA ---M--> GAR

SA ---M--> F

Conclusion GAR some F

SA--M--> F was the sufficient assumption needed to conclude GAR some F

Valid argument 9 https://7sage.com/lesson/valid-argument-form-9-of-9/

You need to be able to work through these intuitively which will come with time, as long as you don't just settle with memorization.

Gotcha; I restudied these after reading everyone's posts from this morning and that actually all made sense ha! I am slowly but surely learning. Thank you so much for the tips. I'll keep at it until I'm a pro

akistotle

I think many MBT questions make heavy use of these types!

@tringo335 said:
In later lessons will JY be showing how to apply validation to specific questions?

Have you done this lesson?
https://7sage.com/lesson/horrific-monsters-mbt-question/
I think in this lesson (and in many other videos) J.Y. shows what is valid or invalid

tringo335

@akistotle said:
I think many MBT questions make heavy use of these types!

@tringo335 said:
In later lessons will JY be showing how to apply validation to specific questions?

Have you done this lesson?
https://7sage.com/lesson/horrific-monsters-mbt-question/
I think in this lesson (and in many other videos) J.Y. shows what is valid or invalid

Nope I haven't yet. Thanks for sharing!

tringo335

@BinghamtonDave @jknauf I was wondering if one of you could help me with a lesson on the CC that I am not getting: https://7sage.com/lesson/quiz-on-drawing-valid-conclusions-2-answers/ On these questions, I understand that we have to affirm the sufficient or the necessary if it isn't already affirmed. So take question 1 for instance, G is affirmed, therefore we need to put a B. Got it. However, on question 3, /U is affirmed, but why do we also put a /B to affirm the necessary instead of just a B?? Furthermore, how do we know which argument needs affirming? In question 1, why does the /H need to be affirmed?

tanes256

@tringo335 for question 1 if you have G then you have B. Then you need to take the contrapositive of G ->B (/B - >/G) to connect it with /H (/B ->/H) to get the some relationship (/Gsome/H).

For question 3 if you have /U then you have /B. Then you need to take the contrapositive of /T ->B (/B ->T) to get /U -> /B -> T.

LeslieKnopeIsMySpiritAnimal

I can totally see how memorizing the valid and invalid forms can be confusing, but I started doing flashcards for it every day. I'm a few months in now and it has really come in handy. I used these flashcards: https://7sage.com/discussion/#/discussion/7890/i-made-digital-flashcards-for-lr-concepts-enjoy that a fellow 7Sager created. Initially, when I would get confused, I'd look at the visual representation that comes with the flashcards - it kind of goes along with JY's bucket explanations. I hope this helps!