LSAT Logical Reasoning in 3 Minutes

Transcript

Logical Reasoning is the heart of the current LSAT. Each question gives you a short argument and asks you to analyse it. The same handful of skills unlock almost every question, so let us build them.

First, separate the conclusion from the premises. The conclusion is the main claim the author wants you to accept. Premises are the reasons offered for it. Words like therefore, thus and so often introduce a conclusion, while because and since often introduce a premise. A quick test: ask which statement the others are trying to prove. That is the conclusion.

Second, assumptions. An assumption is an unstated premise the argument relies on. There are two kinds. A necessary assumption is something that must be true for the argument to work. A sufficient assumption is something that, if added, would guarantee the conclusion. To check a necessary assumption, use the negation test: flip the statement to its opposite, and if the argument falls apart, it was necessary.

Third, strengthen and weaken. To strengthen, pick the answer that makes the conclusion more likely, often by closing the gap between premise and conclusion. To weaken, pick the answer that makes it less likely, often by pointing to an alternative explanation. You do not need to prove or destroy the argument, just move it.

Fourth, recognise common flaws. The most famous is confusing correlation with causation. For example, towns with more ice cream sales have more drownings, so ice cream causes drowning. The flaw is ignoring a third factor, hot weather, which drives both. Another is a sampling flaw, where a small or unrepresentative group is used to judge a whole population, like surveying only gym members about how much the whole city exercises.

Finally, conditional logic. A statement of the form if A then B has one valid inference, called the contrapositive: if not B, then not A. Consider this. If it is raining, the ground is wet. The contrapositive is: if the ground is not wet, it is not raining. That is valid. But reversing it, if the ground is wet, it is raining, is a classic error, because a sprinkler could wet the ground. Negating both parts without swapping them, if it is not raining the ground is not wet, is the same mistake in a different form.

So here is your recap. Find the conclusion, spot the gap an assumption fills, strengthen or weaken by moving that gap, watch for correlation and sampling flaws, and with conditionals, trust only the contrapositive.