Let’s Do Blind Review (PT 59.3.19)

Ok I so want to try something new: a typed report of my blind review methodology. By repeatedly doing this (or something like it) I hope to solidify my understanding of certain question types and increase the speed at which I’m able to dissect them, as well document this process for future reference.

What follows is a copy of a Logical Reasoning question from PT 59 and, after that, my notes from BR regarding the answer choices. When I was taking this LR section timed, I quickly recognized this question was going to be difficult, marked it, and came back once I finished the rest of the section. My original answer choice was (B). After doing blind review, I selected (E), which turned out to be the correct answer. Let’s find out why:

19. If understanding a word always involves knowing its dictionary definition, then understanding a word requires understanding the words that occur in that definition. But clearly there are people–for example, all babies–who do not know the dictionary definitions of some of the words they utter. 

Which one of the following statements follows logically from the statements above?

(A) Some babies utter individual words that they do not understand.

(B) Any number of people can understand some words without knowing their dictionary definitions.

(C) If some words can be understood without knowing their dictionary definitions, then babies understand some words.

(D) If it is possible to understand a word without knowing its dictionary definition, the it is possible to understand a word without having to understand any other word.

(E) if some babies understand all the words they utter, then understanding a word does not always involve knowing its dictionary definition.


So the first thing I did during BR was convert some of the terminology in the passage to shorthand to try to better understand the logical structure I had to work with.

IMG_6152

UW: understanding a word

KDD: knowing its dictionary definition

UOW: Understanding other words


With this, I sought to capture the logical structure as follows:

  1. (UW->KDD)–>(UW->UOW)
  2. (∃x)~KDDx
  3. Therefore, _________

I’m not sure how useful doing this turned out to be (or that I even represented the logical structure of the argument correctly) but in my explication of my thought processes I use the shorthand.


Now for those thought processes:

(A) Some babies utter individual words that they do not understand.

100% False. This would be true IF (UW–>KDD) were true, but it’s only the antecedent of a larger conditional. (KA: Not sure that this is reasoning is correct. But it’s hard to see how this answer choice follows from the stimulus. Actually now that I’ve reread it, I think I’m right; it would be true via contraposition of the antecedent.

If not having knowledge of the dictionary definition of words meant not having understanding of those words, then anyone who uttered a word of which she didn’t know the dictionary definition would utter a word that she didn’t understand. IF.)

(B) Any number of people can understand some words without knowing their dictionary definitions.

This is the answer I chose during the timed section, but I think it’s wrong. It would only be true if the babies understood the words they utter, which they don’t necessarily. And even in that case, the quantifier ANY is very strong and doesn’t follow from the passage. Any baby? Sure. But any people? No…

(C) If some words can be understood without knowing their dictionary definitions, then babies understand some words.

Does not follow. Perhaps there are other requirements for knowing a word. The fact that KDD is false doesn’t mean that babies who utter words understand any of them.

(D) If it is possible to understand a word without knowing its dictionary definition, the it is possible to understand a word without having to understand any other word.

Uhh..no…? (KA: Even though I thought this answer was obviously wrong, I shouldn’t be as lazy with my approach. I should take the time to articulate my reasons for eliminating the answer. Imagine how embarrassed I would be if D turned out to be the correct answer.

In light of this, I’ll now explain why this is answer choice is incorrect: it’s just negating the logical structure without any contraposition.

Take the larger conditional (UW->KDD)—>(UW->UOW).

This answer choice, is in effect saying:

~(UW->KDD)—>~(UW->UOW).

There is no reason to think this is true. It might be, but nothing in the stimulus indicates that it is. If we want the logical equivalent of the passage but with fancy tildes out in front, the contraposition of the original conditional would be:

~(UW->UOW)—>~(UW->KDD)

Ok. At this point I’m ready to say fuck this question, it’s 9:26 on a Saturday night and I’m writing about contraposition and babies who do OR, HYPOTHETICALLY, JUST HEAR ME OUT, do NOT know words. If you’ve made it this far, God bless your soul.)

(E) if some babies understand all the words they utter, then understanding a word does not always involve knowing its dictionary definition.

This has to be true.

If it’s true that all babies do not know the dictionary definitions of some of the words they utter and that some babies do understand all of the words they utter, then it is true that understanding a word does not always involve knowing dictionary definitions.

Christ.