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Inference Questions


Okay, so today what we're going to be looking at is inference questions. And inference questions can be identified by a number of common key phrases that you can see here. Make note of those phrases because they'll help you recognize inference questions on test day. More importantly though, let's talk about what inference questions really do and require of you.

So an inference question requires you to identify an inference. Well, what is an inference? Well, there are two definitions of an inference. Outside of the GRE in real life an inference can be just about anything. Anything that you think might be true, based on information you've taken in. So that's the real life definition of inference.

Now, as you may have noticed the GRE is not real life. And of course the GRE has different rules for inferences and what counts as an inference. So in GRE reading comprehension when you're asked to identify the inference among answer choices, an inference is something that is not directly stated in the text.

So an inference will never simply be a restatement of something in the text. At the same time, although an inference isn't directly stated in a GRE RC passage, an inference can be assumed to be true, based on the text. But we can take it further than that. GRE inferences aren't just kind of half presumed to be true, this might be true. No, what it is, is GRE inferences are inevitably, inescapably true.

They are the only logical conclusion you can draw based on the facts that are stated in the passage. So because inferences are the only logical extension of what has already been stated. They have a very close relationship with the statements that are in the passage. How close? Well, let's look at an example.

So right here we have this example GRE reading comprehension passage about Galileo. And then we have three inferences or proposed inferences. And you want to figure out which of these influences actually would be influences under the rules of the GRE. So if you could pause the video, read the passage, see if you can spot which of the influences are correct and which are incorrect, and then we'll talk about this.

Okay, hopefully you've looked over everything by now. So let's take a look at each of these proposed inferences. The first one, Galileo's telescope was too small to detect the motion of any planet in retrograde. Well, they talk about Galileo's small telescope. So far so good.

And they say the motion of the planet was too slight to be detected by Galileo's small telescope. Well, what's the planet? The planet is the planet Neptune. So here we have Neptune. So what we do know is a Galileo's telescope was too small to detect the motion of Neptune in retrograde.

Now, the question is does Neptune equal any planet? Well, here in real life, you can make an inference that Neptune is a planet. All planets have certain recognizable traits in the sky. Maybe they all behave similarly enough in retrograde but Galileo's telescope couldn't detect any planet. But on the GRE that's too much of a leap.

The passage does not explicitly say that Neptune and all of the other planets were equally difficult to detect because of Galileo's small telescope. So we're going to say that that's actually not a correct inference. Okay, so now let's look at number 2. Galileo showed no interest in Neptune after 1613. Well, let's scan the passage for where 1613 is mentioned.

Okay, so we see 1613 in this first sentence. And we see the Galileo's drawing show that he observed Neptune in 1612, and again in 1613. And this really implies, and we're seeing just just two things in 1612 and 1613. This implies that these are the only two times that Neptune was putting Galileo's drawings.

We have both those occasions and nothing more. So does that mean Galileo showed no interest in Neptune after 1613? Well, if his drawings are the only indication of his interest in something, then yeah, that would be correct. And again, this is a larger leap, a kind of thing you might feel comfortable inferring in real life but not so fast for a GRE inference.

Because for a GRE, remember, you have to have a direct logical extension of the passage. It's the only conclusion you could reach. And here it's not the only conclusion you could reach. You could think, Galileo's drawings are the only indication of his interest. Or you could think, well, Galileo may have expressed interest in other ways.

So because we have that word interest, it's not a direct connection to the idea of drawings. And this again, is not a correct inference. So let's get to the third one. After Galileo's initial observation of Neptune, someone else became the first to identify Neptune as a planet.

This is correct, this is a GRE inference. And the logic, well, it always will be direct, it's not always readily apparent. So what we're going to next is we're gonna look carefully at why this is the only logical extension of something you see in the passage. We can see that this is a true inference based on the first paragraph. So let's take a closer look at that.

So the true inference again, is after kill whales initial observation of Neptune, a different scholar became the first to identify Neptune as a planet. And why is it the case? Well, let's look at this. This is a true inference. Why?

Because Galileo is said to have not been credited with Neptune's discovery because he failed to identify Neptune as a planet. And let's look at that in the passage after seeing that in this first sentence of my explanation here. So it says that Galileo's drawing show he first observed Neptune, that would be the initial observation of Neptune here in 1612.

And it says that he observed it again in 1613 and then made a mistake. He mistook Neptune, and just Neptune by its very definition is a planet. That's the definition of Neptune. He mistook it for a fixed star. And it's said, because of this, hence, he is not credited as the discoverer of Neptune.

So that implies something kind of interesting. It says he failed to identify Neptune as a planet but otherwise, he would have been heralded as Neptune's discoverer. So if Galileo had identified Neptune as a planet, if he had not made that mistake, he would have been the discoverer. And that means at the time there was no other discoverer who would have received credit because if somebody else had discovered Neptune at the time that Galileo first observed it, well, it wouldn't have been possible for him to be credited as Neptune's discoverer under any circumstances.

So Neptune had not yet been discovered when Galileo first observed it. So the discovery, and specifically the discovery that Neptune was a planet, must have come after that observation because nobody had been credited yet. And Galileo not realizing Neptune was a planet was the only thing that stopped him for being credited as a discoverer. So obviously somebody did that later because today we do know that Neptune is a planet.

So again, this is a correct inference. And it is the only logical conclusion you can reach if you carefully read the stated facts in the first paragraph of this passage. So let's review the correct and incorrect inferences that I've linked to this passage. So inference number one, Galileo's telescope was too small to detect the motion of any planet in retrograde.

Now, this is true if other planets show his little motion as Neptune when they're in retrograde. If they behave in a similar way so that the telescope would detect them in a similar way. However, don't think of it as true if. Think of it as incorrect unless this is true, unless planets are completely similar to Neptune in retrograde.

So it's really incorrect unless this is in the passage, and it's not. So in statement number two, Galileo showed no interest in Neptune after 1613. Again we have a true if. This is true if Galileo's drawings are the only measure of his interest. So drawings and interest are directly tethered together this is true, but this is actually incorrect unless the passage says that drawings equal interest.

And it's not in the passage so it's actually incorrect. So we have one and marked off. And now we have three, and three is true because Galileo was gonna be credited as discovering Neptune. And the only reason he didn't get that credit was he thought Neptune was a star, not a planet, which means that somebody else would have gotten credit later when they discovered Neptune was a planet.

So in other words true because of some key ideas in the passage. So we have some true if's and if is never sufficient here for reading comprehension inference question. We have a true because of and you always wanna make sure that there's a specific because. It's cause and effect.

This is in the passage, therefore this is a true inference. So this leads me to a very important concept when you're dealing with influence questions in gre reading comprehension. And that is that you want to look for becauses not if's, when you're selecting the correct inference. In other words true if actually means incorrect.

If you're saying, this is true if this other thing is true which I think might be true but it's not in the passage, then you're really saying it's incorrect. That is not the correct inference you wanna make. You want to say that something is correct because,a correct inference will never hinge on if. Don't speculate, when you speculate that something is correct if an idea that is not in the passage also happens to be true, you're making an inference that is not directly linked to something that is actually in the passage.

So I want to repeat true if really means incorrect and less. And if you can get the hang of that, if you can really get that into your head, you will avoid most of the trappy answers, in theory inference questions. However, there are a few other, well two kinds of really common trappy answers, in theory reading comprehension inference questions, and we're going to look at those trick false inferences next.

Okay, so we're back at this passage and I want you to look at it again. And I want you to check it against the new inferences, I'm suggesting might be valid. Read the passage look at the inferences decide whether they really are valid. So pause the video, do that and then we'll talk about this. Welcome back. Okay, so the newly proposed inferences are Galileo made drawings of Neptune for two consecutive years and telescope technology today is far more sophisticated than it was in Galileo's time.

Let's take a closer look at this. Okay, so we have Galileo made drawings of Neptune for two consecutive years. Well, that definitely seems in line with the passage. So you might say, the passage demands this is true, this must be an inference. But remember the passage has to demand something is true without actually directly stating it.

Is that happening here? Well, not quite. So we have Galileo made drawings and we have Galileo's drawings. Well, if Galileo possesses drawing, so these are his drawings he made them. So this is just a paraphrase, these two underlined pieces are paraphrases of each other.

The drawings are of Neptune because the drawings show Neptune. So drawings that show Neptune and drawings of Neptune are the same thing. So again we have paraphrase in the passage and he did the drawings for two consecutive years. Well 1612 and 1613 if you see that the drawings are made in those two years you are not just inferring logically that they must be consecutive.

They are consecutive by definition, it is a little bit too close we are saying he made drawings in 1612 and 1613, and saying he made drawings for two consecutive years. For two consecutive years, it's just a less specific paraphrase of what's in the passage. So this is a paraphrase.

A paraphrase, and a paraphrase is not an inference. At least not under the rules of Jerry inference questions. So paraphrase does not equal an inference. This is a paraphrase. Even though it's true to the passage, we have to mark it off. It's not a valid inference.

Okay, so let's look at B. B says telescope technology today is far more sophisticated than was in Galileo's time. Well, it's hard to deny that's true. Galileo was around in the 1600s. And everybody knows all kinds of scientific tools including telescopes are more advanced now than they were in the 1600s.

But wait just one minute, the only mention of Galileo's telescope mentioned it as small. It wasn't technologically advanced enough, it doesn't mention or say anything the technology today would have done better. So well you can infer this, you're inferring that technology today is better than it was in Galileo's time, largely from your own common knowledge.

He looked at one year in the passage, maybe two years, and he said, we must be much more advanced by now. But you're inferring that from your own wisdom from your own common knowledge and not from the passage. So common sense or common knowledge. This also is not an inference.

Remember, you want to infer something directly from the passage, a logical extension of the passage, not a logical extension of things you know, even if what you know, is as basic and common sense as how time flows and how things change over time. So neither of these, are valid inferences. And this is another way that GRE will try to.

Now based on our exploration of that passage and Galileo we can arrive at a few big ideas. And if you really internalize these ideas, if you understand them, you'll have really good accuracy on these reading comprehension inference questions. So first idea is that you don't want the correctness of an inference to hinge on an if.

A GRE Reading Comprehension inference is not correct if an unstated assumption is true. The other big idea is that, you do want the correctness GRE and the because, you wanna base your correctness on, a concrete cause and effect reason. A GRE RC inference is correct because the passage directly states a certain thing is true, and the inference must also logically be true based on the stated fact.

Big Idea number three. And inference is not a paraphrase, it's not just a paraphrase of a stated fact, but isn't said a logical extension of a statement the passage makes. And then big idea number four, infer only from the passage. You don't wanna outside knowledge, even if that outside knowledge is obviously true. So, to recap, know if's, focus on becauses, avoid those paraphrases rather, and avoid using outside knowledge to make an inference.

And those four big ideas should serve you well. With that in mind we're going to look at a real GRE passage excerpt or rather a real Maguche theory passage excerpt. And a full question, and we're gonna see if we can use this big ideas to successfully navigate that question. Right, so like I said, we don't have a full passage here.

We have an excerpt, which is the basis for a question. So what I'm gonna ask you to do right now is think of what you've learned in this video. Read the excerpt, read the question, give it the best answer you can, and then we will look and see if you're correct. So pause the video, read answer the question and we'll talk about this Great, welcome back.

Let's take a look at the answers. Okay, so the first thing we wanna say is that A actually is the correct answer. And what does A say, it says that when producing myelin, the human brain does not replace all of its oligodendrocytes at once. So, why is that correct? Well, replacing all the oligodendrocytes at once, we see that toward the end of the paragraph, the oligodendrocytes are replaced not some of them, the oligodendrocytes.

So all of them are replaced when the animal needs to produce more myelin. So that's animal, not human. This is what happens in animal brains and it says that contrasting greatly with human brains. So presumably, if animals do something that contrasting with what humans do, the humans are not doing what animals do, so that's why that's correct.

Okay, so let's look at B. B says, only freshly replaced oligodendrocytes can produce new myelin in the human brain. Okay, so, let's look at the passage itself. The passage says that oligodendrocytes are the cells that form myelin. So oligodendrocytes form myelin, but do they need to be freshly replaced?

Well, in animals they absolutely do. All of the oligodendrocytes are replaced every time an animal needs to replace myelin. So that's definitely the case there, but is it the case of humans? Well, it says that they losses oligodendrocytes less drastically than animals do.

They don't have a full replacement, but they could still be replacing those cells because they need to replace them to make more myelin. Maybe, so, this is incorrect unless human brains and those animal brains replace oligodendrocytes every time myelin is made. Maybe humans don't replace all oligodendrocytes every time myelin is made, but maybe they replace some.

But we don't know that. This is incorrect unless that's explicitly stated in the passage, which it's not. Okay, so let's look at C. C, oligodendrocytes provide other uses to the human brain besides as cells forming the myelin sheaths. Well, C again is clearly an incorrect answer cuz we've already marked A as correct.

So, oligodendrocytes provide other uses to the human brain. Well again, we see this opening sentence that we looked at before that oligodendrocytes are the cells that form the myelin sheaths. There's no mention of oligodendrocytes doing anything else. We just see it associated with myelin. So this is incorrect unless there is an additional unstated purpose for oligodendrocytes.

Or rather unless a statement would be in the passage, you have to mark it incorrect. So C is clearly incorrect, it's just not there. D, the oligodendrocyte life cycle in the human brain differs from that of some mammals. Okay, so we see oligodendrocytes do not perish.

Well, perishing is a key part of the life cycle, so we can say that the idea of the way they perish is a paraphrase of the life cycle. And then it says, this doesn't happen in the same way, does not happen in the same way, that has to do with differs. So we're really seeing this as a paraphrase of the passage. So that is true to the passage but it's not an inference, it's a paraphrase.

E, the number of oligodendrocytes lost in the human brain changes in response to brain trauma. Well, this seems really true like just for common sense. Obviously if the brain is traumatized certain cells will die that wouldn't have otherwise died. But again, common sense is not an inference from the passage, it's not inference by the standards of GRE Reading Comprehension.

So at this point, we have looked at the big ideas for how you can conquer these inference questions. And we've done a practice walkthrough of one passage. And then we've toured an actual full inference question to see how you did. I hope this has been helpful and feel free to review this video and double check things as you're taking on those inference questions in practice

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