Dealing with assumptions is the most critical skill you can develop for the LSAT test. This is the first in a series of lesson articles introducing you to LSAT Assumption Questions. The series includes:

LSAT Assumption Questions

As you already know, an argument contains three parts: premises, conclusions, and assumptions. The premises are stated facts or evidence used to support a conclusion. The conclusion is usually stated, but may be inferred. The assumption is the bridge between the premises and the conclusion. For example, consider the following argument:

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

That’s as simple an argument as you’ll ever see. What’s missing? We know that the main idea, the conclusion, is that Mike is a carnivore (we’re tipped off by the clue word “therefore”). How do we know Mike is a carnivore based on the slim evidence that all dogs are carnivores?

The author must take for granted that we all know who Mike is. Further, the author must take for granted, or assumes, that we know Mike is a dog. If Mike is a dog, and all dogs are carnivores, then it has to follow that Mike is a carnivore too.

The assumption is like missing evidence. You can plug it into the argument where another premise might be, and suddenly the argument looks really tight and convincing:

All dogs are carnivores

+

(Mike is a dog)

=

Mike is a carnivore

If the premise and the assumption are true, the conclusion has to be true. If Mike isn’t a dog, then how can we possibly know that Mike is a carnivore based on the evidence that “all dogs are carnivores?” The author must intend us to understand that Mike is a dog even though that statement is not part of the argument. If we asked the author, “why didn’t you tell me that Mike is a dog?” the author might respond, “Oh, I just assumed you knew that.” A-ha, assumptions.

 Now that you see how LSAT assumptions function, let’s get some practice discovering LSAT assumptions.

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