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Conditional Reasoning

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Joined: Fri May 13, 2011 8:15 pm
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I have read through the entire Logical Reasoning Bible, and I realize that I have a problem understanding Conditional Reasoning. I know and understand the definition of both the sufficient and necessary conditions as well as how to diagram them and the contrapositive. I can also recognize Mistaken Negations and Mistaken Reversals. Furthermore, I am able to use the indicator words to identify both sufficient and necessary conditions. My problem seems to be when conditional reasoning takes place in the actual stimulus or the answer choices and there are no indicator words present. From the definitions of both I cannot seem to figure out which is necessary and which is sufficient by their given definitions (in chapter six) alone. I may get the correct answer 50-60% of the time.

Any help that you can offer would be great.
Dave Killoran
PowerScore Staff
PowerScore Staff
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Joined: Fri Mar 25, 2011 1:18 pm
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Hey Kayci,

The problem you are experiencing is actually pretty common at first. Getting a grip on conditional reasoning is harder than it seems, and it takes a while to develop a strong ability to recognize the exact relationships. I have a few questions/thoughts on the matter:

1. Any chance you could post one or two of the questions that gave you trouble? You don't need to post the text of the question, but rather post the test it is from (with section number and question number) or the location where you found it (page number of the LRB, for example). If I can see a few examples of where you had trouble, it will help me give you more specific advice.

2. Although the definitions of conditionality are helpful, when recognizing it in a sentence it is all about the language. There is almost always some type of indicator or logical formation present that tips you off as to which condition is sufficient and which is necessary. When we look at some of the questions that gave you trouble, I suspect we'll find that there are a few "undercover" words there that will help us figure out which condition is which.

3. One thing to avoid is trying to figure each relationship out based on what you know of the world when you read each sentence. In the real world that works fine, but in the LSAT world that causes a lot of problems because LSAT speakers can make up ridiculous and nonsensical statements.

Here's an example I used in another post on this board:

..... Sentence: The sun rises only if I wake up in the morning.

If you reason this out using your understanding of the real world, you would probably make "sun rises" the necessary condition because it is ridiculous to think that the sun would depend on whether I woke up or not. However, I wouldn't even try to think about it that way during the exam. Instead, I'd see the term "only if," know that that introduces a "necessary" condition, and immediately realize that "I wake up" is necessary and thus that "sun rises" is sufficient, leading to the following diagram:

..... Sun rises :arrow: I wake up in the morning

That diagram and relationship is ridiculous from a real world standpoint, but, nonetheless, that is exactly what the author said in the sentence.

That's a start, but if you can let me know a few of the questions that gave you trouble, I'll be able to give you more specific advice. As I said before, lots of people have this same problem at first, but the good news is that you will definitely be able to overcome it.

Dave Killoran
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