First, they confuse chronological or causal relationships that may be present with the conditional relationship.
Second, they do not distinguish the literal meaning of a statement from those additional understandings we might have in "real life" based on social cues or shared understandings about the intent behind a statement.
Let's examine each of these reasons in turn.
Conditionality Does Not Represent Cause or Timing
Here is an example sentence taken almost verbatim from an actual LR problem.
"Minor tremors occur before every major earthquake."
Does this statement mean that if there are minor tremors, there will be a major earthquake that follows after?
No, it doesn't, although it's easy to think it does.
The word "every" in this statement is introducing the "if" part of this statement, the sufficient condition—major earthquake. So that's why it means: "If there is a major earthquake --> then minor tremors must have occurred before it".
But this *doesn't* mean that any time you see minor tremors, a major earthquake will come after. It's possible for there to be minor tremors that are NOT followed by major earthquakes.
The issue for some students with this example is that they are too focused on the timeline. They recognize that whenever there is a major earthquake, the minor tremors happened before the earthquake. And so they think that this means "minor tremors" should be the "if" part of an "if, then" statement because it's what "leads to" the earthquake later.
But the timing is not what a conditional relationship is about. The chronology of the situation is separate from the question of what condition, if true, is sufficient to prove the truth of the other condition. And that question is answered by focusing on the word "every" in that example. "Every" acts like the trigger—every time a major earthquake happens, then that must mean minor tremors occurred before.
Consider a statement structurally similar to the earthquake example:
"Steven cries every time he watches a Pixar movie."
Does that mean that every time Steven cries, he must be watching a Pixar movie?
Clearly not, he might cry on other occasions, too. It actually means: "If he watches a Pixar movie --> he cries."
This statement is so much easier to understand because of the timeline—first Steven watches the movie, then he starts crying.
In addition, it may be quite natural for you to interpret this sentence as asserting that the Pixar movie is the cause of Steven's crying. (Let's set aside for now whether that statement is in fact making that causal claim.) And so it's easy to think the potential cause—Pixar movie—"leads to" the outcome of crying.
However, the chronology and potential causal relationship involved in this situation are separate issues that an "if, then" statement is not about. Sometimes it happens to turn out that the "if" part occurs before the "then" part, and that the "if" part causes the "then" part. But, as the earthquake example earlier showed, this isn't always the case. Timing and cause don't tell you what means "if" and what means "then".
The Assumed Intent Doesn't Matter
The second big reason some students struggle with conditionals is that they do not distinguish the literal meaning of a statement from those additional understandings we might have in "real life" based on social cues or shared understandings about the intent behind a statement.
For example, your boss says, "I will give you a raise at the end of the year only if you average at least 4 out of 5 stars on customer reviews."
Does this mean that if your average customer review is over 4 out of 5 stars, you will get a raise at the end of the year?
Actually, no.
"Only if" introduces a necessary condition, but we don't know whether there are other things that are necessary in order to get the raise. Maybe the boss also needs to resolve some lawsuits against the company to make sure there's enough money to give you a raise. Maybe the boss also requires you to increase your sales by 10%. Maybe the boss also requires you to get a haircut or learn Japanese.
Some students get confused by that example because in real life, we often use "only if" to emphasize that there's really just one big requirement to fulfill, and we wouldn't normally interpret "only if" as introducing one out of potentially hundreds of other unstated requirements. After all, in real life, if there really were other requirements for a raise, then wouldn't it be reasonable to expect that the boss would tell you about them instead of saying something misleading?
Perhaps that would be reasonable...in real life. In the real world we often presume that people we are speaking to are going to be helpful and would try to provide as much relevant information as they can. And so it's possible that your boss really did intend to communicate that averaging 4 out of 5 stars on customer reviews was the only requirement for your raise.
But the LSAT is asking us to focus on the literal meaning of the boss's statement, and there is no language that tells us there is no other requirement.
Future LSAT Reading Comp Passages
This section of the post collects interesting online articles that you might see edited down to an actual LSAT RC passage in the distant future.
☀️ The Sun Was Dimmer When Earth Formed. How Did Life Emerge? | Quanta Magazine
👶 Babies and chicks help solve one of psychology’s oldest puzzles | Psyche Ideas
🧑🏽⚖️ “New Judgment” and the Federal Habeas Statutes - California Law Review
🎨. Surrealism, the Art Movement That Embraced the Monstrous - The Atlantic