Assumption vs. Inference example Forum

[z0rk]

Just finished the LGB and it is helping me out big time. I am now beginning the LRB. When I attack these books I like to take notes to help myself quickly refer back to learned methods. It helps to carve out pneumonic devices or to phrase things in your own way just to be certain that it will stay within memory. Presently, I have come across a section where the book discusses Assumptions vs. Inferences. Without getting into specifics, I am merely seeking help creating an example to help myself remember the differences of assumptions and inferences in the future.

Kindly please assist me in formulating a sentence or paragraph example that will illustrate the following:

Inferences - these sometimes can be mistaken as something that 'might be true', but on the LSAT an inference MUST BE TRUE. An inference would be a conclusion inferred by the information given in the stimulus

Assumptions - assumptions also MUST BE TRUE; however, on the LSAT they serve the same purpose as a premise that is unspoken for.

These are my own notes and I am merely looking to supplement them with an example that I can refer back to in case I need to re-examine/explain this concept. If the above commentary is incorrect, or, in the alternative, you feel it can be supplemented with more substantial discussion by all means please offer your own take.

Thanks in advance for your help.

[OnlyLivingBoyinNY]

Maybe I can illustrate with an example:

--ImageRemoved--

[OnlyLivingBoyinNY]

But in all seriousness, let me see if I can explain how I distinguish the two.

An inference is something that can be directly understood from the information in the stimulus. Like this: All cats are black. Sammie Davis, Jr. is a cat. An inference is that Sammie Davis, Jr. is black. It must be true, and it must follow from the facts given.

An assumption works a little differently: All black cats are animals that should be petted. Therefore, Sammie Davis, Jr. is an animal that should be petted. An assumption would be that Sammie Davis, Jr. is a black cat. It precedes the conclusion, and without it, the conclusion does not follow.

[tomwatts]

Bear in mind the difference between Necessary and Sufficient Assumptions, too.

Necessary: "The argument depends on assuming which of the following?" (emphasis added)
Sufficient: "Which of the following, if assuming, would allow the conclusion to be properly drawn?" (emphasis added)

You should go about these two in a somewhat different fashion. For example, saying that a Sufficient Assumption "must be true" isn't quite right. Specifically, if I have the argument:

Bob lives in Uplandia. Sally shouldn't date Bob, because Sally shouldn't date evil clowns.

Then a Sufficient Assumption might be that all of the people who live in Uplandia are evil clowns. This goes well beyond what the argument needs and certainly doesn't have to be true, but it would make the conclusion follow, so it is indeed sufficient.

Thus, an assumption is just an unstated sentence that, one way or another, is useful to the logic of the argument. A Necessary Assumption is, well, necessary: it's required, or else the argument falls apart. A Sufficient assumption, on the other hand, is sufficient: it's enough to prove the conclusion, if the premises are true.

An inference is just something that can be concluded if the given statements are all true. This does bring up the interesting issue (rarely of consequence, but occasionally) that the right answer to an Inference question can be a necessary assumption of the argument.

[OnlyLivingBoyinNY]

Assumptions are like pornography: I can't describe them to you, but I know one when I see one

[SanDiegoJake]

Some arguments are about the reasoning of the argument - the connection between the premises/evidence and the main point / conclusion of the argument. Some are not. The assumption is that connection. The correct assumption, when inserted into the argument, will complete the evidentiary link between the evidence and the conclusion. The correct assumption makes the link between the premises and the conclusion. So it concerns the reasoning of the argument as a whole.

An inference, on the other hand, has nothing to do with the connection between the premises and the conclusion. It's just something that must be true based on as little as one statement in the argument (such as the contrapositive of a conditional statement).

Bottom line: To find the correct assumption, ask yourself, "Does this answer choice complete the link between the premises and the conclusion?" To find the correct inference, ask yourself, "Would I bet a million dollars that this answer choice is true?"

[OnlyLivingBoyinNY]

The correct assumption makes the link between the premises and the conclusion.

In LRB terms, what you are describing is a justify the conclusion problem, which is similar to an assumption (what they consider an assumption) but not exactly the same thing.

[mac35352]

The correct assumption makes the link between the premises and the conclusion.

In LRB terms, what you are describing is a justify the conclusion problem, which is similar to an assumption (what they consider an assumption) but not exactly the same thing.

My understanding is that an assumption is an unstated premise of the argument. In the words of the LR bible "the correct answer to an assumption question is a statement the author must believe in order for the conclusion to make sense". The answer will not always link the premises with the conclusion as in the case of Defender Answers that eliminate ideas that could weaken the argument.
I think about it as something the author assumes...duh lol.

[z0rk]

Thanks, this was extremely helpful.

[OnlyLivingBoyinNY]

The answer will not always link the premises with the conclusion as in the case of Defender Answers that eliminate ideas that could weaken the argument.

Right, so in the Sammie Davis Jr. example, by concluding that Sammy Davis Jr. deserves to be petted, I am assuming that he is not a bastard alligator troll, which never deserves to be petted.