LSAT Kung Fu Blog / Half a Dozen Euphemisms for Doing It
Half a Dozen Euphemisms for Doing It
So, one of the important principles tested by the well-fed and amply-proportioned creative team responsible for the LSAT is the distinction between “necessity” and “sufficiency.” We thought we'd think about that for a bit:
Let’s spend some time examining first the terms themselves; second, their relationship to one another; third, the role they play in questions you’ll be asked on the test; and finally, their presence in flaws exhibited by arguments made in the Logical Reasoning sections.
First, some definitions are probably in order. I’m not using these terms in any special or peculiar sense; as you’ll see, good working definitions for both terms will reflect our everyday usage of the words.
“Necessary” means simply that - it means “required.” If something is necessary, then it is essential, it is indispensable, it is inevitable, unavoidable, ineluctable, needed. In other words, you can’t do without it. Being Canadian isn’t necessary for playing ice hockey, but being able to ice skate is. If you can’t skate, you cannot play.
We will likewise use the word “sufficient” on the LSAT in much the same way we do elsewhere: “Sufficient” means “enough.” If something is sufficient, then it is enough to guarantee an outcome or to prove a claim. A sufficiency provides adequate grounds for accepting the truth of a statement. For example, if I were to tell you that I play professional basketball in the NBA, that statement - by itself - suffices for you to know that I am a man. Women aren’t allowed to play in the NBA, so we can all be sure that if I’m in the NBA, then I’m not a woman; I’m a man, and you wouldn’t need any more information than my NBA career to so prove - it suffices.
Now, let’s think about how the terms relate to one another. They obviously don’t mean the same thing, but their use is often related. For example, every formulation of the material conditional indicates the simultaneous presence of both a sufficient and a necessary condition (conditional symbology is also important to your success on the test. Since it’s primarily a visual undertaking, we recommend that you check out our free video lessons on the subject at
http://www.VelocityLSAT.com - at the “Video Library” tab)
(Or at this link: Pages 31-38: Conditional Statements 1 (same as Games Pages 85-93))
The conditional statement indicates that if some one condition holds, then some second condition must also obtain. In other words, if some sufficient condition is present, then some other necessary condition is required as well.
Consider this example (true in the US and much of the world, though there are perhaps some exceptions. Like maybe in Canada. Who knows what goes on up there?):
If you wake up in the hospital after speedballing (injecting an intravenous mix of cocaine and heroin, for those of you with less street cred than me (or who don’t have access to UrbanDictionary.com)) then you, my friend, have taken an illegal drug.
The knowledge that you’ve taken in both cocaine and heroin is sufficient to demonstrate that you’ve intaken illegal substances. If you’ve shot your arm full of those drugs, then it is a required truth that you have introduced illegal substances to your system (“Hello, nervous and venous systems.” “Hello, hard drugs!”).
Or take our NBA example - if you play in the NBA, then you must be a man. Being a man is necessary to playing in the NBA, and playing in the NBA is sufficient to guarantee that the player is a man. The intake of illegal narcotics is a necessary offshoot of doing speedballs, and putting the speedball in your arm is sufficient to guarantee that you’re taking an illegal drug.
Now, let’s consider these terms as they apply to questions we’re asked on the LSAT. There are two ways in which the test writers will ask you to identify information assumed by the arguments in the Logical Reasoning sections of the test. You will be asked to identify assumptions that are necessary to arguments, and you will be asked to identify assumptions that are sufficient for the proof of arguments.
I’ve decided - rather cleverly, I think - to call the first type of question a Necessary Assumption question, and the second type a Sufficient Assumption question.
Necessary Assumptions are asked in the following ways:
Which one of the following is an assumption on which the argument depends [or relies]?
Which one of the following is an assumption required by the argument?
Which of the following is a necessary assumption of the argument?
The argument assumes which one of the following?
These questions demand that you identify a piece of evidence that is missing from the argument, and that has to be there in order for the conclusion to be true.
Consider the following example:
Good lawyers make sound arguments. Lawyers who persuade juries win cases. Clearly, therefore, good lawyers win cases.
This argument makes a claim based on two completely unrelated pieces of evidence. It never establishes that making a sound argument has anything whatever to do with persuading juries. This argument contains the necessary assumption that making a sound argument can - at least sometimes - persuade a jury.
Notice that the argument fails to consider whether bad lawyers make sound arguments, whether good lawyers smell nice, whether lawyers who fail to persuade juries ever win cases, and how much people are paying for their Oolong in Beijing. Again, though, none of those matters have any bearing whatsoever on the central claim about good lawyers winning cases. All of them are missing from the argument. None of them are necessary assumptions. The thing we have to know is whether or not sound arguments can convince juries.
And notice this: adding the fact that sound arguments can influence juries does not prove that good lawyers win cases. Knowing that a sound argument can persuade a jury only proves that a good lawyer - who makes sound arguments - can persuade a jury, not that she necessarily will do so. The information, in other words, is necessary to the argument, but not enough to constitute proof of the central claim.
Contrast that against our Sufficient Assumption question, which is asked in the following ways:
Which one of the following, if assumed, allows the conclusion to be properly drawn?
The conclusion above follows logically if which of the following is assumed?
Which one of the following principles, if valid, most helps to justify the reasoning above?
These questions demand that you identify a piece of information that, if added to the argument, would be enough to demonstrate that the conclusion is true.
Take this example:
Leroy drives a 1987 Trans Am. Therefore, he must also drive the ladies wild.
What? There’s no connection made by this argument between the idea of driving an older Trans Am and driving the ladies wild. This is a poorly constructed argument. If we want to answer the question of what, if assumed, would allow the conclusion to be properly drawn, then it would suffice to say that “Anyone who drives a Trans Am will drive the ladies wild.” That statement, when added to the argument, constitutes sufficient evidence that our pal Leroy does, in fact, drive the ladies wild.
Notice that we don’t have to know that anyone who drives a Trans Am will also drive the ladies wild. Suppose that Leroy drives the ‘87 model, and also that he is handsome, charming, and rich. If that’s all true, and if it’s also true that handsome rich charming guys drive the ladies wild, then it’s certainly not necessary for us to know that just anybody behind the wheel of a Trans Am would be a hit with the ladies, in order to demonstrate that handsome, charming, rich Leroy drives the ladies crazy.
The Sufficient Assumption question demands an answer that will prove that the conclusion is true. That answer does not have to be necessary for the proof of the conclusion. Let’s consider one more example to drive that point home.
Take this argument:
Judy has brown hair. Therefore, Judy plays croquet.
Now, that’s stupid. Obviously not a well-constructed argument. There’s some evidence missing here. Now, consider two formulations of that missing evidence:]
- All brown-haired people play croquet.
- Some brown-haired people play croquet.
Which of those two - (A) or (B) - is necessary to the conclusion of the argument? Think about it.
If you said (B), then congratulations - you’re right. In order for us to prove that brown-haired Judy plays croquet, it is essential that we know that there are some brown-haired people in the world who do play croquet. We have to know, in other words, that brown-hairedness and croquet are not mutually exclusive states of being. However, (B) is nowhere near enough to prove that Judy plays croquet. Just because some brown-haired people play and she has brown hair? Come on - you have brown hair. Do you play croquet? Right. Only knowing that some people play just isn’t enough to show that Judy must play.
However, answer (A), if true, would suffice to prove that Judy is a croquet playa’. If she has brown hair, and you tell me that all people with brown hair play croquet, then, by god, Judy must know her way around the old mallet n’ wicket (uh, that's what she said).
So (A) is clearly sufficient to prove that Judy of the brown hair does play croquet, but it also is not necessary. Think about it - to prove that some one person plays croquet, do I really have to know that everyone else does? Again - you have brown hair. Do you play croquet? Would I really need to demonstrate that you play croquet in order to prove that Judy does? Of course not.
See? What is necessary to a conclusion is not always sufficient to prove that conclusion. What is sufficient to prove a conclusion is not always necessary for the proof of that conclusion.
And this brings us to our final point; the misuse of these concepts as a typical flaw pattern on the LSAT. A central belief at Velocity LSAT is that your best test preparation involves the heavy use of pattern recognition. One strong pattern on this test is the recurring appearance of a small group of typical flaws. We'll eventually touch on all of them at some point in the life of this podcast; if you'd like a quick overview of the lot, you can find that at http://www.VelocityLSAT.com, in the free section of Logical Reasoning videos at the "Online Classes" tab.
(At this link: http://www.velocitylsat.com/video/flaw-types-p95-part-1-causal-flaw )
One recurring error of reasoning on this test is the confusion of a necessary for a sufficient condition (or vice versa). This error looks like this:
Anyone who has had carnal relations with Leroy knows that he drives a bitchin' Trans Am. Jaclyn has admitted that she recognized the car as belonging to Leroy; thus, she must be lying when she says that she has not known him (in the biblical sense).
To conclude that Jaclyn has bumped nasties with Leroy simply because she knows he drives a Trans Am is to commit the Necessary v. Sufficient Conflation. We have taken a sufficient factor for knowing that he drives a Trans Am (if you’ve done the horizontal mambo with Leroy, that’s enough for you to know what car he drives) and we have confused that factor for being a necessary factor (we’ve acted as though in order to know what kind of car Leroy drives, you must have knocked boots with him).
So, now you maybe know a little bit more about necessity and sufficiency than you did before (and a whole lot more, maybe, about Leroy than you wish you knew). Understanding these terms, their relationship to each other, and their misuse as a typical flaw in the Logical Reasoning section goes some distance toward your becoming a fierce logician and a master of LSAT Kung Fu.
For more, check us out online or drop us a line at Info@VelocityLSAT.com, and visit The Forum (http://www.VelocityLSAT.com/Forum) to join the conversation, to give us more euphemisms for doing it with Leroy, to tell us how disgusted you are by the thought of euphemisms for doing it with Leroy, or to suggest topics for future conversations.
Until next week, stay bitchin’.