LSAT 105 | Section 4 | Logical Reasoning: Q8

LR Question 8 Explanation

QUESTION TEXT: Linguist: Only if a sentence can be diagrammed …

QUESTION TYPE: Flawed Reasoning

CONCLUSION: Speaker X’s sentence will be deemed grammatical by speakers of the language.

REASONING:

1. If Grammatical ➞ Can be diagrammed
2. If Grammatical ➞ Recognized as grammatical
3. Speaker X’s sentence can be diagrammed.

ANALYSIS: The rules are:

Grammatical ➞ Can be diagrammed

and

Grammatical ➞ Recognized as grammatical

We know Speaker X’s sentence can be diagrammed. What does that actually allow us to conclude? Nothing!

“Can be diagrammed” is necessary for being grammatical, but it is not sufficient. For all we know, you could be diagrammable but still be ungrammatical.

Yet the author concludes: Recognized as grammatical.

The author is assuming because it can be diagrammed ➞ Grammatical. And if we know it’s grammatical, we know it will be recognized as grammatical. So they conclude it will be recognized as grammatical.

But the issue there is that we can’t conclude it actually is grammatical.

___________

1. Whether most people can diagram sentences properly doesn’t affect whether the sentence can actually be diagrammed. A math problem can be solved even if most people are bad at math and probably wouldn’t solve it correctly.
2. CORRECT. This identifies the missing possibility: some ungrammatical sentences might still be diagrammable. If that’s possible, then Speaker X’s sentence being diagrammable doesn’t prove that it’s grammatical.
3. This says “recognized as grammatical” sentences can be diagrammed. But the argument needs to move from diagrammable to recognized, so this goes in the wrong direction.
4. This just restates the first rule: grammatical sentences can be diagrammed. The flaw is that the linguist reverses that rule.
5. Some ungrammatical sentences being recognized as ungrammatical doesn’t affect the argument. The issue is whether a diagrammable sentence must be grammatical, and this doesn’t address that.