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Is every assumption the argument makes a NA?
sammmm93
Alum Member
I think I reasoned my way though this as I wrote it out. Figured I’d post it in case anyone might be helped by it. Please point out any issues.
I get that every NA is an assumption the argument actually makes. Why? bc for an argument to work, the NA must be true which entails that if the argument has a NA, the argument is obviously making that assumption. But is the inverse also true? Is every assumption the argument actually makes a NA?
My understanding is that most SAs are assumptions we impose on the argument, not ones that the argument actually makes. Sometimes the assumption the argument makes happens to also be a SA. Eg
P: A
C:B
A->B is the NA as well as SA. This seems to affirm every assumption argument actually makes is a NA.
Is it wrong to think of SAs as assumptions we impose on the argument?
Are there times an argument actually makes an assumption that isn’t necessary? I guess technically there could be an assumption within a stimulus or argument that’s unrelated or irrelevant to the conclusion’s reasoning and therefore it being false wouldn’t wreck the conclusion and isn’t needed. LSAT typically doesn’t do this though.
Okay I think I figured this out. Just bc the argument assumes something doesn’t make it a NA but every NA is something the argument assumes. So to check whether a NA Q ac is wrong, ask if the arg assumes that AC. If it doesn’t then eliminate. 8/10 times if argument does assume AC, it’s the correct ac. That’s typically what I do when I’m a bit unsure on NA Qs instead of negation test. More intuitive for me.
Comments
The short answer to your question is yes, everything the argument assumes is a necessary assumption.
I think the confusing issue you're running into is one of the big downsides to calling something a "sufficient assumption."
In the LSAT instruction/studying community, we've taken to calling some assumption questions "Sufficient Assumption" and others "Necessary Assumption".
This suggests that there are two kinds of assumptions. But logically speaking, that's not truly correct. There's only one kind of assumption: necessary assumptions. Anything that the argument assumes is a necessary assumption. In fact, outside the LSAT context, there's no such thing as a "necessary assumption" - there's only an assumption. They're one and the same. If something isn't necessary for the argument to assume, then the argument isn't assuming it.
So what, then, is a "sufficient assumption"? It's simply a statement, that if true, would guarantee the conclusion. Sometimes that statement happens to be also a necessary assumption. Other times that statement is not an assumption of the argument, but is just an idea that if true, guarantees the conclusion.
For example,
Premise: sammmm93 studied for the LSAT for 3 months.
Conclusion: sammmm93 will get a 180 on the LSAT.
"Anyone who studies for the LSAT for at least 1 day will get a 180 on the test."
That statement is sufficient to guarantee the conclusion. But it's not a necessary assumption, and logically speaking, we shouldn't even call it an assumption of the argument at all.
But then why do we call it a "sufficient assumption"? Simply because that's what LSAT instruction has taken to calling it. Basically, because the question stem of SA asks for what answer, "if assumed", makes the conclusion logically follow, we've taken to calling these questions "Sufficient Assumption" questions.
(If it were up to me, I'd push back on this classification. Have you ever noticed that some strengthen question stems use the phrase "if assumed"? But we don't call these "Strengthen Assumption" questions, do we? So it's odd that we call some questions "Sufficient Assumption".
I believe this is the reason Powerscore actually calls SA questions "Justify" and NA "Assumption". I think this classification is a good one, since SA questions aren't really asking for what the argument assumes, in the ordinary sense of the word "assumes". In some ways, SA questions are really more like "Strengthen-Plus" questions - strengthen, but in a way that guarantees the conclusion. Arguably they have more in common with Strengthen than with NA, although there are definitely good reasons to think of them as similar to NA, too.)
Good point ^. I suppose they should just be called sufficient premises/statements/ or whatever. The question would ask: which one of the following statements guarantees the conclusion?
Makes a lot more sense.
It's unintuitive to call SAs SAs, in my opinion. Depending on your internal monolog, it may be easier to make a pet name for SA questions (maybe something like guarantee questions) and totally remove the "assumption" idea completely. In that case, you could use your intuitive, day-to-day understanding of what assumptions are and project it onto NA questions with little to no adjustment on how you reconcile them within yourself when you compare day-to-day usage of assumptions to what NA are within the scope of the LSAT.
Furthermore, I think the hardest part to reconcile regarding SA questions is that they are set in a "the author is 100% correct, but they forgot to mention something that you need to remind them of in order for them to be 100% correct" universe, and our day-to-day understanding of assumptions is mostly never like that. When have you ever been in a situation where you know what someone else says is 100% correct, they fail to mention key aspects of it, and you correct them on the spot solidifying their "argument" to the point of validity? Probably not very often. It's alien compared to normal usages of "assumptions".
In normal, daily assumptions (NAs), someone is either making an unstated assumption (ex: did you just assume my gender by pointing me towards the ladies room!?), or they are literally saying that they are assuming something (ex: let's assume you're right in your idea about how box office sales are tanking, but that doesn't explain why Ben Aflick is out of work). SAs takes this idea and sheds it apart because it makes YOU tell the SPEAKER that they are ABSOLUTLY CORRECT, and furthermore that they FORGOT to mention something (aka the NA).
Thank you all for your responses! All very insightful and helped clear things for me. I completely forgot about this post. I made one night at like 2am when I couldn’t fall asleep loll
I’m not getting all the hating on sufficient assumptions. They are totally real assumptions which were identified as far back as Aristotle. They are a staple of formal logic, and necessary assumptions rely on their relationship to a sufficient assumption to exist. For every necessary assumption that exists, a sufficient assumption must also exist.
Can you elaborate? My view is that a particular statement can be necessary for the argument to be valid, sufficient for it to be valid, or both. But the word "assumption" has a particular definition that is in line with what we traditionally think of as "necessary assumptions". This means that there are some things that LSAT teachers/students might call a "sufficient assumption" that are actually not assumptions of the argument.
For example,
Gary is 7 feet and 2 inches tall. So, he must be good at basketball.
The following would be identified as a "sufficient assumption" in the LSAT community:
"Anyone who is over 6 feet and 6 inches tall must be good at basketball."
But you would agree that this is not actually something the argument assumes, right? So in that sense, we call it a "sufficient assumption", but the word "assumption" in that usage is really just a stand-in for the idea of "statement". It's a statement that, if true, is sufficient to make the argument valid.
Hi, appreciate the breakdown. So are you saying:
Assumption = propositions that are necessary for a given argument to be valid
'Sufficient Assumption' = propositions that could justify the conclusion OR proportions that could justify the conclusion and necessary for a given argument to be valid
So 'Necessary Assumption' is actually redundant and 'sufficient assumption' is really a misnomer because, taken literally, it only covers the latter part of its definition?
But they are assumptions, it's just a question of how they're applied. An assumption--sufficient or necessary--does not mean something someone making an argument is assuming. There is that application, but it's not the way we apply it in the study of conditional logic. A necessary assumption is one which must be true if the argument is going to have any chance of being validated. But it may just be a flawed argument. Similarly, a sufficient assumption is one which, if assumed true, would validate the argument. Just like with necessary assumptions, the argument need not assume it. We're not trying to identify assumptions the author is actually making. Our task is a more formal, objective assessment. If we were to assume that anyone over 6'6" must be good at basketball, then we would validate the argument. The assumption is one that we ourselves are extending to the argument, not one we are identifying the argument to have actually made.
I kinda figured SA was something more like a strengthening question as well. And I definitely do see some SA questions where the right answer choice could act as an NA and it trips me up sometimes. It's just odd to me that SA is probably my best LR question type and NA is my worst.
But @sammmm93 I really like the end of your post about thinking about NA ACs as if this is what the argument is assuming. My performance on SA and NA are polar opposites, and in general I'm just least confident in NA questions and going through the AC's.
I get the sense that you're using "assumption" to refer to the way in which we assume that a statement is true and then evaluate the impact of that statement's truth on the argument; if it's sufficient to make the argument valid, then it's a "sufficient assumption". I don't think that's any different from how I think of the situation, except that I think using the word "assumption" in that context is liable to confuse given that the word "assumption" also has another meaning referring to unstated premises of the argument, which is what I think you're referring to when you mention "identifying [assumptions] the argument [] actually made". And to me this latter definition is what I think most would have in mind when it comes to the topic of assumptions, which is why I think it makes sense to drop usage of the word "assumption" when it comes to sufficient assumptions. What is lost by thinking of them as "statements", that if true, make the argument valid? (I wouldn't actually drop this usage given how ingrained it is; it may be more confusing not to call something SA now that people accept that terminology.)
What's interesting to me is that, if I'm understanding your use of "assumption" here, then under that approach wouldn't you also think of Weaken questions as "Weaken Assumption" questions and Strengthen questions as "Strengthen Assumption" questions and Resolve/Explain questions as "Resolve/Explain Assumption" questions? After all, in all of those problems, we're being asked to assume that the answers are true - which answer, if assumed true, has the appropriate effect on the argument or situation? In the same way that you noted with SA we are evaluating the impact of "assumptions ... that we ourselves are extending to the argument", in a Weaken question, wouldn't we be evaluating the impact of "assumptions" (called such by virtue of our assuming the truth of the statement) that we ourselves extend to the argument? Only that with Weaken we're looking for an "assumption" that weakens?
@kolerv9923-1 thanks! It works for me. It’s what I did to get a 172 on this June’s test!
Hi!
My first time posting on here. So excited I think I can answer your question.
A necessary assumption is not every assumption an argument makes but a specific type of assumption that when the conclusion is true, these assumptions have to be true, too. A necessary assumption is something that necessarily has to be true if the conclusion is true. You can think of it as a something that has to be true to support the conclusion of the argument.
For example:
Conclusion: Maddy can't wait to eat her delicious food tomorrow morning.
NA: Maddy will be able to eat tomorrow morning.
In my example, you can see that if the conclusion is true, the NA HAS to be true, too.
A question you can ask yourself to find the NA is: If the conclusion is true, must this NA also have to be true?
I hope this helps
@MADDYDOMEK Hey thanks for your response, though I’m not sure the NA in your example is correct. Even if Maddy doesn’t have the ability to eat tomorrow morning for whatever reason, she can still be eagerly waiting to eat.
A better version of your example, I think, would be:
C: Maddy will eat delicious food tomorrow morning.
NA: Maddy will be able to eat tomorrow morning.
Notice that the necessary assumption is still defined by its relationship to the sufficient. The sufficient, for the purposes of NA questions, is exactly like you said: "If the conclusion is true." This is exactly right. Without the sufficient, there is no necessary.
I'm not sure about your example though. You could be really excited about eating your delicious breakfast tomorrow and then die during the night. That doesn't mean you couldn't have been excited. I think a better NA would be something like, "Maddy has reason to believe that she will be able to eat tomorrow morning." But your larger point is the much more significant one and is really insightful. I ask people all the time what the sufficient is to the NA answer choice, and no one ever seems to know.
Yeah, these are all necessary assumptions given the sufficient assumption that the answer choices are true. That's why you'll always see some form of, "which one of the following, if true, . . ." There's your "if." There's your sufficient. The difference is most of us don't struggle to conceptually satisfy that sufficient. It's a very comfortable and natural assumption to make for the purpose of answering LSAT questions. So it's not that helpful to frame these this way.
I also just want to be clear that none of this is "my" use of "assumption." It is the way I am using it, but I am not claiming that it is "mine" or to have done anything but adopted the conventions of formal logic.
This is also not a convention made up by LSAT teachers. This is 2,300 years of the formal study of logic going back to Aristotle. I am not arguing my personal viewpoint on this. I am arguing what Aristotle and Bertrand Russell and every other logician I've ever heard of viewed as an assumption. Even Wittgenstein, who wouldn't think any of this matters, would recognize the ancient convention. But Wittgenstein I think is a good place to end on. Wittgenstein wouldn't think the actual words we use much matter: Resolving the differences between meaning and expression in language is one of the primary jobs of philosophy, so what we call something really isn't that important as it has no effect on the actual meaning. What matters here is that you get it. I get it too. Our disagreement is over the language used to express the same, correct idea. I think it takes a lot of chutzpah to push against Aristotle and thousands of years of convention which has withstood scrutiny by some of the greatest minds humanity has produced, but I can't say that I see anything incorrect in what you've said given the way you've defined your terms.
Really I just want to emphasize that this isn't one of those LSAT things created by LSAT teachers to dumb things down for the more limited purposes of the LSAT. This is the real thing from the real study of formal logic. From there, call it what you like so long as you understand it.