Weaken the Argument: Some Strategies and Examples

“Weaken the argument” questions in the Logical Reasoning section of the LSAT can be slow going. In almost every case, a “weaken” question makes a bad assumption, but these assumptions can be hard to spot. If you can see a chink in the argument when you first read the stimulus, you’re in luck. Check the answer choices for something that expands on that.

If you can’t spot the flaw on your first reading, it’s time to read the answers. In general, the right answer will be something the author fails to consider or takes for granted. “Weaken” questions require you to use your imagination as well as your reason–it helps to put yourself into the situation and visualize how things would change as you read through each answer choice.

The following examples are logically equivalent to real LSAT test questions. Only the nouns, verbs, adjectives, adverbs, pronouns, punctuation, tone and context have been changed for copyright reasons.

Widget Maker: The Widget 109 has been a dog ever since we introduced it, but we have a new ad campaign: “The Widget 109 is awesome. Buy one now!” I know, I know, it might not work, but it’s our only chance to make this thing pay. We should try it!

The correct answer is: “Advertising for the Widget 109 would require dangerous cutbacks in other advertising.”

Here’s another “weaken” question:

Terra cotta sewer pipes are relatively inexpensive, but they develop cracks over time that allow tree roots to enter and clog the lines. Septic engineers stopped using terra cotta pipes over ten years ago, but pipes keep getting clogged. This proves that the type of pipe makes no difference to the risk of root blockage.

The correct answer is: “Root blockages usually occur in pipes that have been in place for several decades.”

Here’s another:

Ravens are exceptionally intelligent birds, and may be able to think strategically. A wild raven nicknamed “Poe” discovered a deer carcass and made a series of loud calls. Other ravens flocked in and started eating the deer. When Poe discovered a dead raccoon a few days later, he made no noise. This shows that Poe learned he needed to keep silent to keep the food for himself.

The correct answer is: “Ravens typically call to other ravens whenever they find large amounts of food.”

Next:

There are various techniques for increasing reading speed. Some yield immediate results, while others require longer training times.  In a recent study, participants who tried the “immediate results” approach read faster, and so did those who tried the more time-consuming approach. This shows that time-consuming approach has no value.

The correct answer is: “People who combine the two approaches read faster than people who use either of them separately.”

Even with the right answer right in front of you, it can still be very hard to achieve certainty on a “weaken” question. When in doubt, zero in on the conclusion. A conclusion generally has two terms (logicians call them the “subject” and the “predicate”). Can you find both of them elsewhere in the stimulus? If there’s a term in the conclusion that doesn’t appear elsewhere in the stimulus, it has been assumed. Look for that term in your answer choices–the right answer will include it. The wrong answers may not.

If you can match up the subject and predicate in the conclusion to similar terms in the premises, make sure the terms in the premises are identical to the terms in the conclusion, One slippery question had “salary” in the premise and “financial rewards” in the conclusion. The correct answer revealed that an employee’s “financial reward” consists of salary plus significant employee benefits.