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# THE ONLY

Alum Member
in General 414 karma

How would you diagram “the only thing you need for A is B ” and “the only way to have C is through D”?
Are these two the same statements?
I’m starting to feel like, at least the first one, is a bi-conditional. Thoughts?

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• Member
35 karma

“The only thing you need for A is B.”
First, one can see that B is a sufficient condition for A, so B → A.

Can or must B also be a necessary condition?

“The only thing you need to get a car is lots of money.”
[lots of money → get a car]

But is this necessarily the same as
[to get a car → lots of money]?

You might be able to get a car without having lots of money if you can receive it as a gift, so it is not the case that [to get a car → lots of money], and hence it should also not be the case that [A → B] in the original example.

“The only way to have C is through D.”
Here, it seems that D is the necessary condition and C, the sufficient condition.

I didn’t notice it before, but they seem to be contrary statements or statements of mistaken reversal, as some would call it?

• Alum Member
edited June 2020 313 karma

How would you diagram “the only thing you need for A is B ” and “the only way to have C is through D”?

For the first one, you do it like this: A → B

For the second one, you do it like this: C → D

Are these two the same statements?

Yes, they are essentially the same

I’m starting to feel like, at least the first one, is a bi-conditional. Thoughts?

No bi-conditional in either one of those above unless you had stated:

“the only thing you need for A is B ” and “the only way to have B is through A”

I hope this helps!

• Alum Member
111 karma

@dudener "the only" is a group 1indicator, and it introduces sufficient conditions. So I believe the sentence "The only thing you need for A is B" is diagrammed as A--> B rather than B --> A.

• Member Administrator Sage 7Sage Tutor
edited June 2020 4473 karma

I've brooded over this question many times and it's kept me up at night. This is the conclusion I came up with and I hope it helps.

"The only thing you need for A is B"

First, I don't think it's as simple as just A and B. The part of the sentence that "The only" is describing is "a thing you need for A", not just "A" itself.

So the translation can be, in full terms using "the only" as a group 1 conditional indicator:
"If it's a thing you need for A, then it is B".
This statement is entirely different from saying "If A then B".

BUT ALSO, you might have noticed there is a necessary condition in this statement as well. It's the word "need". This statement is saying for A to be true, you need B.

So you can also translate it as "If A, then B". And this translation works too.

So, I would not say that it's a biconditional. For it to be a biconditional, you need the same two ideas in both conditional statements, just switched around. We have two conditionals, but the ideas are not the same. "A" and "A thing you need for A" are not the same idea.

I do however think that this sentence somehow gives us two conditional statements in one sentence. But the conditional statements it gives us do not meet the criteria for it to be a bi-conditional.

Let me know if you have any questions or feel free to pm me!

• Alum Member
414 karma

Thanks everyone who commented! Despite the conflicting answers, I do think that I am getting the hang of it!

@Christopherr so just so I understood you correctly, it's like putting "the only thing you need for A is B" into the standard form of "the only A is B" right? So the only As (thing you need for A) is B"?

• Alum Member
edited June 2020 401 karma

"the only thing you need for A is B"

A --> B

You NEED B to have A, B therefore is necessary

"the only way to have C is through D"

C --> D

You NEED D if you're going to have C, D is therefore necessary.

Those who argue the inverse above are wrong. When a clause is prefixed anytime with "the only" it will always introduce the sufficient condition.

It will happen on tougher LR questions that the writers will sneak in conditionality without using our ingrained indicator words, but just by describing a relationship with conditionality. An example is "As X increases, Y increases." Therefore More of X --> more of Y. When you are at a loss for which direction a conditional is going or whether there is a conditional at all, try and breakdown if there is a relationship of necessity in the statement, it could help net you some free points.

• Member Administrator Sage 7Sage Tutor
edited June 2020 4473 karma

@"caffeine powered human" yes. If your A is defined as "a thing you need for A" then that works!

Looking back at this more, on a timed test I think the best way to diagram this would be A ---> B, (defining A as A and B as B ) and to take 'the only' as to mean B is the sole requirement that A needs, so there are no other necessary conditions needed to satisfy A. However, it doesn't give the same weight as a biconditional because this definition allows us to have B's and still not have A's.

Let me know if this makes sense!

• Alum Member
414 karma

Gotcha!! Thanks to you both @EveryCookCanGovern @Christopherr

• Monthly Member
edited June 2020 383 karma

Something that helped me perfect identifying which group "the only" belongs too was saying "the only is the only (in group 1)." Every other usage with the word only will identify a necessary condition, or group 2.