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When we say an argument is "good," what do we really mean? Well, recall that an argument is just premise(s) plus conclusion. Premises supports the conclusion and the conclusion is supported by the premises. So, “good” really just describes how well the premises support the conclusion. In other words, “good” describes the strength of the support relationship between the premises and the conclusion. Just how “good” can the relationship be? Until it becomes perfect, of course. When that happens, it is said that the argument is valid. Turn your attention to the chart below:
To weaken any argument on the LSAT's Logical Reasoning section, you have to understand one thing.
This thing is not tangible nor obvious. It’s instead abstract and subtle – which means it’s hard to understand. Here it is: You have to take away the support. What support? The support that the premises give to the conclusion. Please read that again. It may sound very obvious, but you’d be surprised at how often you will fall prey because you didn’t heed this warning. It’s only nature since our instinct when arguing is to deny our opponents’ premises. He asserts that there are bugs in the kitchen and therefore an exterminator visit is in order. You deny his premise by asserting that there are no bugs in the kitchen. But what would be the point of asking a question like this? All you did was to say “no.” Much more interesting is it to concede to your opponent her premises and then try to argue that despite your concession, her conclusion still doesn’t follow from her premises. That’s what Weaken (weakening) questions test you on. It most certainly does not say that you are to contradict, attack or weaken a premise nor does it ask you to contradict, attack or weaken the conclusion. It says you are to deprive the support that the premises give to the conclusion, as if with magic. Let me illustrate. Did you watch Dragon Ball Z growing up? Remember Goku’s Kamehameha?
Necessary assumptions can wreck an argument.
First, let’s understand what a necessary assumption is. It’s an assumption (definition: unstated premise) that is necessary for the argument. “Necessary” here means the same thing it does when we talk about a “necessary condition” (as opposed to a “sufficient condition”). Let’s put the relationship between argument and necessary assumption in Lawgic and then run the contrapositive.
Argument (valid) –> Necessary Assumption (true)
/Necessary Assumption –> /Argument
In English, this means that when we negate the necessary assumption, the argument falls apart. No necessary assumption, no argument.
Necessary Assumption questions present you with an argument (premises + conclusion) where in order for the conclusion to be valid, there is a necessary (critical) assumption not stated in the argument. Without this particular assumption, the argument falls apart. Your job is to find this sucker, a necessary assumption, in the answer choice.
There are two types of Necessary Assumptions (NA).
I cannot over-stress the importance of being able to identify premises and conclusions on the LSAT. Not only that, but to do it fast. But, we gotta start somewhere so slow is better than not being able to do it at all. Here are three distinctive slow ways that students have found very effective.
As a learning device, this is good. You can rely on these. But, take this caveat to heart. You can’t consciously rely on these three devices. At the end of the day, you have to internalize all of it. It has to be very, very quick. Intuitive. You read the passage and you just know that this is the premise and this is the conclusion. Somewhere in the back of your mind, one of these three devices is operating subconsciously and telling you what the premise is and what the conclusion is.
This game is difficult because of its bi-conditional rule. Of course, if you are a conditional logic master, then this game will be easy for you. It's the one about The Export Alliance, which consists of Nations X, Y, and Z, and which of the following five crops they export: oranges, rice, soybeans, tea, and wheat. It's from LSAT PrepTest 45, December 2004, Section 3, Questions 18-22, Logic Game 4.
Watch the video lesson below and learn how to solve this game easily.
For more Logic Games explanations like this one, hop over to our Logic Games page. There, we've recorded video explanations for every Logic Game going back over a decade. All in HD, with variable playback speed, and you get to ask questions. Oh, the best part: it's completely free.
LSAT Conditional Logic GROUP 2 is made up of the following terms:
- Only if
- Only when
- Only where
All the words in this group follow this translation rule:
The ideas introduced by (i.e., immediately following) these words are the necessary conditions.
Let’s try it:
This logic game is easier than it looks. It's the one about an animal shelter that places six dogs - greyhound, husky, keeshond, Labrador retriever, poodle, and schnauzer - with new owners on Monday, Tuesday, and Wednesday. It's from LSAT PrepTest 44, October 2004, Section 3, Questions 7-12, Logic Game 2. A lot of students consider this to be one of the toughest LSAT Logic Games of all time—let's break it down!
This game hides behind an important inference and it tries to confuse you with two conditional rules. Watch this video lesson and learn how to solve this game fast.
LSAT Conditional Logic Group 1 is made up of the following terms:
- The only
All the words in this group follow this translation rule:
The ideas introduced by (i.e., immediately following) these words are the sufficient conditions.
Let’s try it
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