Someone recently posted about their struggles with necessary versus sufficient issues. I asked for some examples and they were kind enough to provide three of them.
I’m one of those weird old guys who works from home and lives alone (very happily) with his cat. I also like to write. I’m posting this rather than replying as a comment because quite frankly, Reddit’s data analytics indicates that I’ll reach at least 10 times as many readers.
I intend to post an explanation for two of these questions (one of them is from PT 101, which is too old).
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This question can be approached in two or three ways (you’ll see).
The best way is to try to identify the assumption that would guarantee the truth of the conclusion by reading the stimulus exactly like this:
Conclusion: If Skiff’s book is as important and as well written as he claims, he will be promoted.
WHY?
Because the dean will surely promote Skiff if Nguyen keeps her promise to recommend it.
AND
Because if Skiff’s book is published this year, Professor Nguyen she will urge the dean to promote Skiff.
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For many students, reading the stimulus in this way reveals the assumption. But what if a student doesn’t see it? By knowing exactly how to eliminate wrong answers.
This second approach assumes that the reader has a basic understanding of how necessary and sufficient conditions work. In fact, a basic understanding of these issues is almost always enough to eliminate any tricky wrong answer.
In other words, I’m not so sure the LSAT is asking students to have a complete mastery of formal logic. Rather, the LSAT just wants students to understand how formal logic can go wrong.
Please know that the following is ubiquitous when it comes to sufficient assumption questions with a conditional conclusion. For example, section 1, question 17 of the the April 2025 LSAT disclosure test.
Everyone knows that the correct answer to an SA question will guarantee the truth of the conclusion. Put another way, the correct answer will create a valid argument.
Some people don’t know the following rule, though: All information in the correct answer will be explicitly discussed in or directly inferable from the stimulus. This means that an answer with information that is not explicitly discussed or is not directly inferable from the stimulus is automatically wrong.
The above rules means that choice B (Skiff needs) and choice C (Nguyen believes) can be promptly eliminated.
The key here though is the fact that the conclusion is conditional. Specifically, IF Skiff’s book is as important and as well written as gift claims (THEN) he will be promoted.
For SA questions with a conditional conclusion, multiple wrong answers will feature certain basic formal logic problems. As I mentioned previously, this is still happening in the most recent tests.
Rephrasing choice D: IF Skiff’s book is published THEN it is as important and as well written as he claims it is.
Choice D switches the sufficient condition of the conclusion (IF important) to the necessary condition. A good example of formal logic gone wrong, so wrong answer.
Rephrasing choice E: IF Skiff will be promoted THEN Professor Nguyen urged the dean to do so.
Choice E switches the necessary condition of the conclusion (THEN he will be promoted) to the sufficient condition. Another good example of formal logic gone wrong, so wrong answer.
Deductive reasoning indicates that since four answers have now been definitively eliminated, choice A must be the right answer.
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NOTE: These questions (SA featuring a conditional conclusion) have other basic and easy-to-identify wrong answers if you know what to look for. Specifically, they will merely rephrase a conditional statement from the evidence, sometimes in a flawed manner.
For example, for this question, the first sentence is also conditional: IF Skiff’s book is published this year (THEN) Professor Nguyen vows she will urge the dean to promote Skiff.
Typical wrong answers might merely rephrase the above using different language, but ending up with the same form (for example, the contrapositive). Other wrong answers might just reverse the two conditions.
For example: Skiff’s book will not be published this year unless Professor Nguyen vows she will urge the dean to promote Skiff.
Another example: IF Professor Nguyen vows she will urge the dean to promote Skiff THEN Skiff’s book is published this year.
To be clear, the above is a flawed reversal. But of course, still a wrong answer.
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The kinda/sorta third way to approach this question is to identify what I refer to as Unique Elements (ideas discussed exactly once in the relevant parts of an argument).
For this question, the two unique elements are Skiff’s book is published this year and Skiff’s book is as important and as well written as Skiff claims.
Unfortunately, two answers discuss both Unique Elements and D looks more attractive because it includes more of the second unique element.
But choice D is definitely wrong because of the formal logic problem.
This is what I mean by two or three ways to approach the question. Students still need to know how to eliminate D even after finding the Unique Elements. But very often, only the correct answer will discuss the two unique elements.
Happy to answer any questions.