Yesterday, I was yelling about one of the LSAT's dirtiest words: "Should." Today's lesson includes another LSAT profanity... a foul two-word combination that will--if you're attacking the test correctly--inspire in you a GlennBeckian level of outrage.
Here's the argument. Be critical, and see if you can get pissed! If you can get pissed, you're on the right track.
Ethicist: On average, animals raised on grain must be fed sixteen pounds of grain to produce one pound of meat. A pound of meat is more nutritious for humans than a pound of grain, but sixteen pounds of grain could feed many more people than could a pound of meat. With grain yields leveling off, large areas of farmland going out of production each year, and the population rapidly expanding, we must accept the fact that consumption of meat will soon be morally unacceptable.
Put your personal political leanings aside. The point isn't whether you, personally, think meat is right or wrong. The point is that the argument's facts don't justify its conclusion. Tell me: Where does the argument go completely off the rails?
If you said that the argument melted into a pile of steaming bullshit at the words "morally unacceptable," you are 100% correct. Morally unacceptable? MORALLY unacceptable? By whose morals? Yours? Mine? Glenn Beck's? There are no general standards of "morals" on the LSAT. The argument provides no definition of what's "morally acceptable" or "morally unacceptable." Instead, it just concludes that something is "morally unacceptable" on the basis of facts about agriculture and human population. If you're doing it right, when you read "morally unacceptable," you said "oh, you can fuck right off with that."
If you're pissed, you're 90% of the way to answering the question. Let's see what that question happens to be:
Which one of the following, if true, would most weaken the ethicist's argument?
No sweat. We already know that the argument sucks because it uses "morally unacceptable" in the conclusion without providing any evidence that tends to define that term. This should be easy... all we have to do is pick an answer that points out this glaring flaw.
(A) Even though it has been established that a vegetarian diet can be healthy, many people prefer to eat meat and are willing to pay for it.
This answer provides evidence that people want to buy meat, but that's not the same thing as proving that meat is morally acceptable. Let's look for a more punishing weakener.
(B) Often, cattle or sheep can be raised to maturity on grass from pastureland that is unsuitable for any other kind of farming.
Interesting. This wasn't at all the direction I was going, but if this is true then "grass" is an alternative to "grain." Looking back at the argument, I can see that the entire thing was about grain. If there's an unexplored alternative that the argument didn't mention, then doesn't that tend to undermine the argument? This might be the answer.
(C) If a grain diet is supplemented with protein derived from non-animal sources, it can have nutritional value equivalent to that of a diet containing meat.
Huh? This is beside the point. Who cares if a grain diet, properly supplemented, can be nutrionally equivalent to meat? What's that have to do with the argument? And anyway, this could only be a strengthener, since it's pro-vegetarian. We're looking for a weakener. B is still best so far.
(D) Although prime farmland near metropolitan areas is being lost rapidly to suburban development, we could reverse this trend by choosing to live in areas that are already urban.
Metropolitan areas? Suburbia? WTF is this even talking about?
(E) Nutritionists agree that a diet composed solely of grain products is not adequate for human health.
Again, health is simply not the issue.
Our answer is B, because it's the only answer that tends to undermine the argument's conclusion that "meat is morally unacceptable."
The point of this lesson isn't that arguing with the speaker will allow you to predict the answer to every single question. The point is that arguing will allow you to understand the argument. Once you understand the argument, most questions are pretty easy to answer.