Knock a hole in that argument.
What does it mean to weaken an argument? A lot of tough weaken questions will be much easier if we clarify what, exactly, it takes. Let’s start off with an argument.
Randy is planning on asking Sandy out next week. Randy has a luscious, flowing mullet (the hairstyle, not the fish). Therefore, Sandy will almost certainly say yes.
The assumption underlying this argument is that Sandy really digs mullets. So it would weaken the argument if, for example, Sandy thinks mullets are gross. That part isn’t too hard.
But what if I told you that Sandy has no preference for any one hairstyle over another? If that were the case, we’d have no indication whether Sandy would say yes or no. Would that weaken the argument?
It would. If you didn’t think so, it’s time to correct one of the most common misconceptions about weakening arguments. LSAT students often think that since we generally accept an argument’s premises, the answer to a weaken question has to attack the conclusion. If Sandy thinks mullets are gross, then she’s not terribly likely to say yes.
But the prompt for a weaken question doesn’t usually ask for evidence against the conclusion. Typically, the LSAT asks you to weaken an argument. To attack an argument’s reasoning, aim for its assumptions. In our example argument, Randy’s mullet was supposedly the reason Sandy would say yes. If Sandy cares not one bit about hairstyles, that attacks the assumption that Sandy digs mullets.
Sure, Sandy might say yes for other reasons. If Sandy doesn’t care about Randy’s mullet, Randy, as far as we know, is on equal footing with anyone else who might ask Sandy out. But Sandy’s lack of preference among hairstyles attacks the logic of drawing the conclusion that she’ll say yes from the premise that Randy has a mullet. That means it weakens the argument.
On easier weaken questions, the answer often seems to go against the conclusion. But on harder questions, the correct answer might not give evidence against the conclusion. You can prepare yourself to spot those answers by clearly identifying the argument’s assumptions before you look at the answers. If an answer attacks an assumption in the argument, it weakens the argument.