Self-study
If understanding a word always involves knowing its dictionary definition, then understanding a word requires understanding the words that occur in that definition. ███ ███████ █████ ███ ████████████ ████████ ███ ████████████ ██ ███ ████ ███ ██████████ ███████████ ██ ████ ██ ███ █████ ████ ██████
The Stimulus
The first sentence is a conditional, but an unusual one. Both the "if" part and the "then" part are themselves conditionals:
If understanding a word always involves knowing its dictionary definition, then understanding a word requires understanding the words that occur in that definition.
This might make intuitive sense. If understanding "ephemeral" requires knowing the definition ("lasting for a very short time"), you'd also need to understand "lasting," "short," and "time."
The critical word is if. The stimulus isn't asserting that understanding a word requires knowing its dictionary definition. It's telling us what would follow if that were true. The "if" part may or may not be true. We have no idea. Just like "if it rains tomorrow, I'll bring an umbrella" doesn't tell you whether it will rain, the first sentence doesn't tell us whether understanding actually requires knowing dictionary definitions.
The second sentence gives us a straightforward fact: all babies utter words whose dictionary definitions they don't know. A baby might say "mama," "dog," or "correlation" without being able to define any of these words in dictionary terms.
Anticipation
You might feel like these two sentences should combine to produce an inference. But they don't, because the stimulus doesn't tell us whether babies understand the words they utter.
WORDS THEY UTTER
🗣️
"mama" "dog" "more"
✓ confirmed
DICT DEFS THEY KNOW
📖
missing for some
✗ not all
WORDS THEY UNDERSTAND
🧠
?
❓ never stated
The stimulus tells us babies say words and don't know the dictionary definitions of some. It never tells us whether babies understand any of those words. Maybe they do, maybe they don't.
You might feel like the word "but" before the baby fact signals some kind of contradiction with sentence 1. That might help you get to the right answer, but as a logical matter, there isn't any inference we can make right now from combining the two statements in the stimulus. No specific prediction is possible, so we'll use process of elimination.
19.
Which one of the following ██████████ ███████ █████████ ████ ███ ██████████ ██████
a
Some babies utter ██████████ █████ ████ ████ ██ ███ ███████████
This requires accepting a claim the stimulus only presents as hypothetical. If you're drawn to (A), you're probably reasoning like this: understanding a word requires knowing its dictionary definition, so babies who don't know dictionary definitions must not understand those words. The problem is the first step. We don't know that understanding requires knowing dictionary definitions. That claim appears as the "if" part of sentence 1. It's a hypothetical. "If A then B" doesn't tell us A is true.
If it turns out that understanding doesn't require knowing dictionary definitions, then babies might understand every single word they say. We have no way to rule that out. If (A) had said "If understanding a word always involves knowing its dictionary definition, then some babies utter words they don't understand," it would have been something that must be true.
b
Any number of ██████ ███ ██████████ ████ █████ ███████ ███████ █████ ██████████ ████████████
This could be false. If the "if" part of sentence 1 happens to be true (understanding always requires dictionary definitions), then nobody can understand words without dictionary definitions, and (B) is false. Since (B) could be false, it can't be something that must be true.
Even setting that aside, "any number of people" is very strong. Even in a world where some people can understand words without dictionary definitions, we wouldn't know that any number of people can do this. Maybe only certain people can, while others still require dictionary definitions.
c
If some words ███ ██ ██████████ ███████ ███████ █████ ██████████ ████████████ ████ ██████ ██████████ ████ ██████
Nothing in the stimulus connects babies to the words that might be understandable without dictionary definitions. You might be tempted by real-life intuition: if some words can be understood without dictionary definitions, those are probably easy words like "mama" and "dog," and you're thinking that babies understand those. But that line of reasoning isn't coming from the stimulus.
We don't know which words, if any, can be understood without dictionary definitions. What if those words happen to be "jurisprudence," "entropy," and "sarcasm"? There's no reason to think babies understand those. And even if the words overlapped with what babies say, "can be understood without a dictionary definition" just describes a property of the word. It doesn't mean every person who utters that word actually understands it. A word being understandable without a dictionary definition and a baby actually understanding that word are two different things.
d
If it is ████████ ██ ██████████ █ ████ ███████ ███████ ███ ██████████ ███████████ ████ ██ ██ ████████ ██ ██████████ █ ████ ███████ ██████ ██ ██████████ ███ █████ █████
This reverses the direction of the conditional. Sentence 1 tells us: if understanding requires dictionary definitions, then understanding requires understanding other words. (D) essentially claims the reverse: if understanding does not require dictionary definitions, then understanding does not require understanding other words. But "If A then B" does not mean "if not A then not B."
e
If some babies ██████████ ███ ███ █████ ████ ██████ ████ █████████████ █ ████ ████ ███ ██████ ███████ ███████ ███ ██████████ ███████████
This must be true. The stimulus tells us babies utter words whose dictionary definitions they don't know. (E)'s "if" clause adds the claim that babies understand all the words they utter. Put these together:
FROM STIMULUS: Babies utter words they don't know the dict def of
+
(E) SUPPLIES: Babies understand all words they utter
↓
COMBINED: Babies understand words they don't know the dict def of
↓
CONCLUSION: Understanding does not always require knowing the dict def
Notice something interesting: this reasoning doesn't use sentence 1 at all. The entire proof comes from combining (E)'s "if" clause with the baby fact in sentence 2. The LSAT made this question feel harder than it needed to be by leading with a complicated embedded conditional that the correct answer doesn't even touch.
Also notice the contrast with (A). Both answers involve the question of whether babies understand the words they utter. But (A) flatly asserts that babies don't understand some of those words, which we can't prove. (E) puts its claim behind an "if" and only asks what follows if babies understand all of those words.