# Critical Reasoning Assumption Questions – Let’s Play Jenga!:

by on March 15th, 2018

Some Critical Reasoning question types are pretty straightforward about what you’re being asked to do. On a Strengthen the Argument question, for example, many students naturally have a good sense of what they’re supposed to do even if they’ve never specifically studied the question type before.

Critical Reasoning Assumption questions are a bit less intuitive, but I’d like to show you a technique that makes them a lot easier to unscramble. Let’s try a GMATPrep question first: Set your timer for 2 minutes and give it a go.

Excavations of the Roman city of Sepphoris have uncovered numerous detailed mosaics depicting several readily identifiable animal species: a hare, a partridge, and various Mediterranean fish. Oddly, most of the species represented did not live in the Sepphoris region when these mosaics were created. Since identical motifs appear in mosaics found in other Roman cities, however, the mosaics of Sepphoris were very likely created by traveling artisans from some other part of the Roman Empire.

Which of the following is an assumption on which the argument depends?

(A) The Sepphoris mosaics are not composed exclusively of types of stones found naturally in the Sepphoris area.
(B) There is no single region to which all the species depicted in the Sepphoris mosaics are native.
(C) No motifs appear in the Sepphoris mosaics that do not also appear in the mosaics of some other Roman city.
(D) All of the animal figures in the Sepphoris mosaics are readily identifiable as representations of known species.
(E) There was not a common repertory of mosaic designs with which artisans who lived in various parts of the Roman Empire were familiar.

Step 1: Identify the Question (Read the Question First)

We’re being asked to find “an assumption on which the argument depends.” What that means is that one of the answer choices is secretly performing a keystone role in the argument, even though it’s not actually in the argument. (An assumption is an unstated premise that permits the argument to stand.) In other words, the right answer is something that the argument needs in order to have a chance of being valid.

Step 2: Deconstruct the Argument (What Was the Argument About?)

There are some mosaics in this ancient Roman city with pictures of animals, but most of those animals weren’t native to that region at the time (Premise 1). Other mosaics in other Roman cities show the same animals (Premise 2), so the mosaics were probably created by traveling artisans from other regions (Conclusion).

Before going any further, make sure you follow the intended logic of the argument. The author is claiming that since these mosaics included pictures of exotic animals from far away, the artists must have been from far away too.

Step 3: Pause and State the Goal (Brainstorm / Try to Predict the Right Answer)

For any Critical Reasoning questions that are part of what we call the “assumption family”—assumption, strengthen, weaken, or evaluate—you always want to try to kick the tires on the argument before looking at the answer choices. Looking at this argument, I’m not all that convinced yet. Just because the animals depicted were from far away doesn’t necessarily mean the artists had to be from far away too. Maybe the artists were locals who read about the exotic animals in a book, or heard about them through the grapevine.

Step 4: Work from Wrong to Right (Go to the Answers and Use Process of Elimination)

Remember, we’re looking for something that would need to be true in order for the argument to have any chance of working—and the argument is that the artisans who made these mosaics were probably travelers from far away.

As we work from wrong to right, let’s just do a first pass and eliminate anything that’s clearly not needed by the argument. If anything sounds like it might be needed, then let’s hold onto it for now.

a) The Sepphoris mosaics are not composed exclusively of types of stones found naturally in the Sepphoris area. The mosaics are not made of all local stone. Maybe the mosaics were made elsewhere (not by locals) and then transported to the city? That would potentially impact who was making the mosaics, so let’s hold onto that.
b) There is no single region to which all the species depicted in the Sepphoris mosaics are native. The exotic animals depicted aren’t all from one region. Who cares? Eliminate.
c) No motifs appear in the Sepphoris mosaics that do not also appear in the mosaics of some other Roman city. All of these motifs in the Sepphoris mosaics also show up in some other mosaics in other cities. I’m not totally sure how that might affect our argument yet, so let’s hold onto it for now.
d) All of the animal figures in the Sepphoris mosaics are readily identifiable as representations of known species. We don’t need that to be true for the argument to work—they could have included pictures of dragons or unicorns too, but I don’t think that would affect the argument one way or another. Eliminate.
e) There was not a common repertory of mosaic designs with which artisans who lived in various parts of the Roman Empire were familiar. This relates to the idea we talked about that locals maybe knew about exotic animals from a book or something. Hold onto this.

Step 5: Use the Assumption Negation Technique (Play Jenga)

Okay, we’re down to 3 possible answers: A, C, and E. Now it’s time for a move that applies only to Assumption questions—don’t use this on any other Critical Reasoning question type. It’s called the assumption negation technique, but I like to think of it as playing Jenga.

You’ve played Jenga, right? You build a tower of little wooden blocks, and then you try to take out one block at a time without the tower falling down—when the tower falls down, game over.

That’s what we’re going to do here, except the argument is the Jenga tower, and the answer choices are the wooden blocks. What we’re going to do is negate one answer choice at a time (the equivalent of removing that block from our Jenga tower) and see if that destroys the argument (makes our tower fall down). If you pull out a block and the tower fall down, then the tower needed that block.

Similarly, if you negate an answer choice—reverse its meaning—and that makes the argument fall apart, then that means that the argument needed the original, unaltered version of that answer choice in order to stand. I know it’s a bit topsy-turvy, but trust me—it’ll make perfect sense once you see it in action.

You negate each answer choice by reversing the main verb or action in the sentence, usually by insertion or deletion of the word “no” or “not.” (Make sure you only negate each answer choice once—don’t insert ‘no’ in multiple places in one answer choice.)

Of our remaining three answers, we’re now looking for the one that, when negated, destroys the argument (makes our Jenga tower fall down).

A) The Sepphoris mosaics are not composed exclusively of types of stones found naturally in the Sepphoris area. If the mosaics are made of all local stone, we still don’t necessarily know who made them—local artisans or traveling artisans. Our Jenga tower is still standing.
B) There is no single region to which all the species depicted in the Sepphoris mosaics are native.
C) No (Some) motifs appear in the Sepphoris mosaics that do not also appear in the mosaics of some other Roman city. Notice I only eliminated the first ‘no’ (replacing it with the word ‘some’), but not the second. The negated version of this answer means that there are some motifs that are unique to the Sepphoris mosaics. I suppose that slightly undercuts the idea of traveling artisans, but it doesn’t make it impossible—maybe traveling artisans came in, made the mosaics, and included a little custom Sepphoris symbol for the local clientele. It’s a bit of a stretch, but it works. Our Jenga tower wobbled a little, but it’s still standing.
D) All of the animal figures in the Sepphoris mosaics are readily identifiable as representations of known species
E) There was not a common repertory of mosaic designs with which artisans who lived in various parts of the Roman Empire were familiar. If there was a common repertory of designs that artisans from all over knew about, and if those designs included a variety of exotic animals from various regions outside of Sepphoris, then the whole argument just fell apart. It didn’t have to be traveling artisans who made the mosaics; it easily could have been locals who simply knew the common designs even if they had never seen those animals in person. Our Jenga tower just fell over, and E is the right answer.

So, to recap: Only use assumption negation on Assumption questions, and do it only after you’ve eliminated the obviously incorrect answers. It’s easier to knock out a couple first, as we did here, and then negate the remaining choices, rather than negate all five answer choices on every problem. Once you get used to the process, the right answer will start to jump off the screen at you, and you’ll be far more confident about Critical Reasoning Assumption questions.