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Inference Questions

An inference on the GRE is subtle. It’s a very tricky question, which is exemplified by the fact that it comes up a lot on the harder section. But, what exactly is an inference as far as the GRE is concerned? Well, it’s a statement that you can make based on the information in the text. It is very similar to implying, also a common question at harder levels.

The idea is that something’s not directly stated but what is being implied is closely tied to the text. Now I like those definitions to an extent, generally speaking. But they miss something. What exactly does closely mean? And what do we mean by based on the text?

And this is what makes the GRE inference questions so tricky. For a valid inference on the GRE it is one that must be true on the information in the text not one that could be or might be true. So, if something seems like it kind of is, it’s most likely not a valid inference on the GRE. So, let’s take a look here.

Here’s a little excerpt and, based on this excerpt, what can we infer? Let’s start with example one. And you may actually want to pause this and actually read the excerpt. Okay, so example one. The brains of humans and the brains of mice are very different. Duh.

Guess what though? Is that a valid GRE inference? Well, does it say that in the passage? Well it says that they’re very different as far as the oligodendrocytes in myelin creation or generation goes. That’s just one facet of the entire brain.

So therefore can we infer that they are very different? Not in the GRE. That assumes way too much, even though common sensically you might wanna answer yes. Interestingly though, scientists use mice and rat brains cuz they’re not all that together different from human brains. So sometimes you can assume quite a lot.

Example two in regards to myelin production, the human brain tends to differ from that of mice. Now this is nice and specific. We’re going to myelin production which is what is going on here. And notice very different versus tends to differ. Softer language backed up clearly by the text.

That’s a valid inference. Not one that takes a whole lot of logic mind you, sort of obvious but definitely a valid one. Example three, the human brain loses cells that are not categorized as ODs. So I’m thinking about it and I’m imagining that ODs can’t possibly be the only cells we have in our brain and we lose brain cells all the time.

Hee hee, I’m losing brain cells now sorta thing. So, of course that must be the correct answer, but it’s not found in the passage. It can be completely 100% true in the real world. Everyone agrees with this. It’s documented, etc. But, if it’s not found in the passage, you can’t just jump to this conclusion.

Example four, the human brain loses the ODs, albeit not as many as mice and rats do. Okay, well what do we have here, is the idea that inferences aren’t always this direct. Does it say that the human brain loses ODs, yes, not as many as mice and rats do, yeah they lose them all the time.

So we’re not really arriving at an inference, we are just describing what’s in the passage. So it’s important to know the two differences. You’re arriving at a conclusion based on the information in the text. So it’s combining two chunks of information and equaling something that is 100% true.

That is airtight. That cannot be argued. Let’s have a look at what that would look like. The human brain does not need to replace oligodendrocytes to produce myelin. Does it say this anywhere here? Notice the question before said it directly, so we didn’t really even have to infer that.

But this is not stated anywhere. What is stated is that human brains lose 1 per 300 cells every year. And that’s a state very different from the OD state in mice and rats, in which every time myelin is needed, they need to replace the oligodendrocytes. And so if that contrasts greatly with what’s found in humans, we can infer, what?

That the human brain if it needs to make more myelin, it does not need to replace oligodendrocytes. It can use the existing ones. And again, it barely loses any, each year just a few, but they’re always on store ready to go whenever the brain needs them. That is not stated, but it is 100% airtight.

And this is a classic GRE inference. And it’s tricky to wrap your head around it, and I encourage you to do a couple things. Well obviously watch the video again if necessary, but also go through the official guide and look at some of the inference questions or questions where it says implication or the author is implying.

And look how did inferences aren’t directly stated, but have to be true based on what is stated. So that is the important part, not explicitly stated in the text, and it doesn’t require any leaps in logic. And this is interesting. You’ll find yourself trying to make answer choices work sometimes and thinking well based on this it was probably the case.

And the more you feel you have to make these leaps or these probablies or these kind of statements the more likely you are not dealing with a GRE inference, but you are dealing with a wrong answer. Okay. Let’s take a look now. Based on this passage here, or this excerpt from the long passage, let’s take a look at an actual inference question.

And I encourage you again to read this and then pause it. Pause it, read it and then of course unpause it and we’ll go through the question together. Okay, here it is. Regarding ODs and myelin sheaths in the human brain, it can be inferred that. Now this one’s a little tricky.

It’s nice to be able to answer the question right off the bat, but there’s a lot of text here to sift through. So this one of those cases where I would actually have you go through the answer choices. And that’s why it’s so important as well to know how the GRE tries to trick you on wrong answer questions.

The way we just went through those examples, the ones weren’t correct or valid inferences would be classic wrong answer choices on an inference question. Let’s take a look at A. Not all of the ODs are used at one time to form myelin sheaths. Well, we go back here and it says that in human brains, the oligodendrocytes are always on hand, they’re always on supply.

Which is different from the rat brains. So therefore not all of them are used at the one time in the human brain, that seems like a pretty safe inference. I’m going to put a check mark next to it. B, new oligodendrocytes must be formed in order to provide more myelin. Well, is this the case in the human brain?

No. So be careful. B is true based on the passage, but that would be an answer to a question based on rats and mice brains. And so we, of course, we’re dealing with the human brain and therefore, B is wrong. And so far our only contender here is answer choice A.

So let’s move on. C, ODs provide other uses to the brain besides as cells forming myelin sheaths. This is one of those common sensical ones. Hm. They must provide other uses to the brain but we can’t infer it because it’s not stated anywhere.

And we can’t draw that logical inferential thing without making some crazy leaps of logic and without basing it on common sense. D, an average human brain will lose most of his or her, an average human not human brain, will lose most of his or her oligodendrocytes in a life time. Guess what? Sounds like common sense as well.

But if you look there, it says one out of 300 per year you’d have to live to a very, very ripe old age and then some. So obviously, not the answer. Finally E, the number of ODs required to produce myelin changes in response to brain trauma. Hm. You read that again.

It sounds right. It has the ring of truth. And so, what you want to do is to remember your wrong answer traps. That was covered in a previous video as well as common wrong answer traps, as far as inference questions go. Let’s read that one more time and be careful.

The number of ODs required to produce myelin changes in response to brain trauma. Probably would. Right? Because you need a lot of new ODs to replace the myelin because something has happened.

Brain trauma so maybe the number goes up or its the speed at which they replaced increases or maybe I’m making leaps of logic here. I’m bringing in the word maybe, kind of, I am basing it on what I think seems to be how the brain operates. But I don’t know that much about the brain. And what I know is really based on this passage, and that’s what should be guiding my decision.

And therefore E is out and A is our answer.