Yesterday, I began my question-by-question response to the free LSAT distributed by LSAC: June 2007. Go ahead and print yourself a copy of that test so you can follow along with me. The single most important thing I can teach you about the LSAT Logical Reasoning is to begin every question by saying "This argument is bullshit because _______________." If you can fill in that blank, you are 90% of the way toward answering any type of Logical Reasoning question. You've really got to dig in your heels here. The arguments you will see are intentionally incomplete, flawed, and sometimes outright incoherent. If you don't understand an argument, it's usually not because you're dumb. It's usually because the argument makes no sense. Your task is to understand and articulate why the arguments make no sense.
The argument presented in Question 2 starts with a fact about Labs (they all bark a lot). Then it presents a fact about Saint Bernards (they all rarely bark). Then it says Rosa's dogs are all Lab/St. Bernard mixes. Then, predictably, it makes a dumbass conclusion about how often Rosa's dogs bark. Can you tell me why this argument is bullshit?
It really doesn't matter here whether the conclusion says the dogs bark all the time, or never bark, or "bark moderately." The problem is that crosses can have different characteristics from either of two purebreds. Since Rosa's dogs are crosses, we really can't make any conclusion about them. The facts only give us evidence about purebreds.
The argument here is just like saying "all monkeys are good climbers but bad swimmers, and all fish are good swimmers but bad climbers, so this cross between a monkey and a fish will be a moderate swimmer and a moderate climber. Does that make sense? Um, no. I'm not a biologist, nor does the LSAT require me to be. But common sense says we just can't predict how such a hybrid would turn out. This is the same problem with the logic about Rosa's dogs.
The Question asks us to find an answer choice that demonstrates a similar flawed pattern of reasoning. So the correct answer must be 1) flawed and 2) flawed in the same way. Before you go on to the answer choices, it's probably useful to see if you can come up with a similar example like my monkey/fish example above. Give it at least a few seconds, then take a deep breath and move on to the answers.
A) My problem with this answer choice is the word "some" in the second sentence. The argument about Rosa's dogs never used "some"... it was all or nothing. So I'm very skeptical that this will turn out to be the correct answer. Remember that 80% of the answer choices are, by definition, incorrect. Start with the presumption that the answer choice you are reading at any moment is probably not the answer. The instant something about an answer choice smells fishy, we should move on. We can always come back if necessary, but we should only reconsider A after reading all the other answer choices and deciding that none of them are any good.
B) This looks perfect to me. Type A is very toxic, but Type B is nontoxic, therefore a blend of the two will be "moderately toxic"? How on earth would we possibly know that to be true? I think the mix could be either very toxic, or not toxic at all. (Just like Rosa's dogs might bark constantly, or never.) This is a bad argument, and it's bad in the same way as the given argument. This looks like a great answer.
C) There's no flaw here. If all the facts are true, then the conclusion must also be true. Remember we're looking for a flawed answer choice. So this can't be our answer.
D) This might be flawed, in that Bob could be 90 years old and maybe he has forgotten both shorthand and calculus. Anyway, even if this is flawed it isn't similarly flawed, because there's nothing here about blending two things together and having an outcome that is a hybrid of the two initial things. B is still the best answer by far.
E) This is definitely flawed, because there are surely a million people who make great dresses besides Kenisha, and a million people who make shitty dresses besides Connie. But again there is no "mixing" going on here. I am very confident that B is our answer.
I'd love your feedback on these responses. Please leave comments, or email email@example.com.