Since the assumption of an LSAT argument is the unstated portion of the argument, a key skill for the LSAT test is finding the hidden assumption. What is it that the author intends or implies but does not say outright?

This is the second in a series of lesson articles introducing you to LSAT Assumption Questions. The series includes:

Discovering LSAT Assumptions 

There are three ways of detecting assumptions. One is by using intuition, one is by making a bridge, and the other is by applying an objective test. The intuitive method is faster, and you will gain accuracy with it as you gain familiarity with the test. Making a bridge takes a little longer, but works well, especially if you’re good at making simple paraphrases of an argument. The objective test takes longer, but will always give you the right answer.

Typically, you use the intuitive method to form a prephrase. If you’re intuition doesn’t kick in while you read the argument, you can trim the argument down to a careful paraphrase and then build a bridge. If you have to eliminate answer choices, you can plug them in using the objective test. You wouldn’t want to test every answer choice — it would just take too long. But if you’ve narrowed your choices down, you can pick out an assumption with confidence using the denial test, the litmus test of all assumptions.

Let’s break these methods down one-by-one.

Intuition and the Red Flag

You’ve already seen the intuitive method. As you read an argument, something will seem wrong about it. A red flag pops up in your mind and that flag is related to the central assumption. Very few arguments on the LSAT are completely logical. Most of them contain at least on central assumption, and most of the assumptions are somehow flawed. You have a feel for why the argument is wrong, and you use that intuition to guide you to the assumption. Again, consider this simple argument:

All dogs are carnivores. Therefore, Mike is a carnivore.

You might read that argument and think, “wait a second, I don’t know anything about this Mike guy.” That points you to the gap that needs to be filled. What is the connection between Mike and dogs, or Mike and carnivores. Then it clicks, “I get it, Mike must be a dog.” The red flag points you in the right direction. Even if you don’t get it completely clear, at least you know the scope of the assumption. It has something to do with the connection between Mike and dogs and carnivores.

Building a Bridge

The next method falls somewhere between using your intuition and applying the objective “denial test.” If you can build a careful paraphrase-the simpler the better-you can compare the elements in the argument. Then the task is relatively simple. You need to bridge the dissimilar elements and ignore the similar elements. Again:

All dogs are carnivores. Therefore, Mike is a carnivore.

Remember step two of the TestSherpa four-step method for Logical Reasoning? Read and paraphrase the stimulus (step one is to read the question stem). You need to make a paraphrase of every stimulus. You don’t necessarily have to write it out, but at least think about the argument in your own terms. Your words are easier to work with than the test maker’s words. Let’s say you wrote out a paraphrase for this argument in your test booklet:

Dog = Carnivore  →  Mike = Carnivore

What is similar in both the premise and the conclusion? Carnivore. You don’t need to bridge carnivore to carnivore. What is dissimilar? Dog and Mike. Those are the elements you need to bridge. The assumption must connect dog to Mike: Mike is a dog.

This seems fairly easy using this simple argument, but as you get better at the TestSherpa method, you can apply it to sophisticated arguments as well. The key is learning to paraphrase the argument as simply as possible. The best way to learn that is practice and study. Sorry, there’s no shortcut.

Next we’ll take a look at the final, objective and often favored way of finding LSAT assumptions and checking their fit: The Denial Test.

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