Normal full-term babies are all born with certain instinctive reflexes that disappear by the age of two months. Becau...

AnkitM February 6, 2016

Question regarding argument structure

I understand the question, but I diagrammed the structure a bit differently. I put NFTB -> RDB2 (normal full term baby -> reflexes disappear by 2) and then the cp being both negated and reverse so, not RDB2 -> not NFTB. I chose answer D because the both terms were both negated and reversed. Am I doing this wrong? Should I be looking for a valid argument structure not just matching up just whether the NC is negated in one statement, and then seeing that another statement has the NC not negated and making that question wrong. If I had the original statement as NFTB -> not IRA2mos, then I wouldn't have picked answer D because the the NC (animal pouches) is not negated. So should I just focus on argument structure (valid statement and valid contrapositive)?

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Mehran February 6, 2016

@AnkitM the key here is realizing that this is a valid contrapositive argument and then finding the answer choice that parallels this reasoning.

The only difference between our diagram and yours is what you chose to use to represent "reflexes disappear by age of two months" (we used not IR @ 2 mos; you used RDB2).

PR: NFTB âž¡ï¸ RDB2
not RDB2 âž¡ï¸ not NFTB

P: not RDB2
- - - - - - -
C: not NFTB

PR: NFTB âž¡ï¸ not IR @ 2 mos
IR @ 2 mos âž¡ï¸ not NFTB

P: IR @ 2 mos
- - - - - - -
C: not NFTB

Hope this helps! Please let us know if you have any other questions.

Kellan September 27, 2018

I diagrammed my similarly to AnkitM.
P: NFT - RD2M

Mehran, looking at your set up, you have, P2 as: "P: not RDB2".
I had the premise and conclusion written exactly like you, except for the "not" on the second premise. How is it "not RDB2"? I wrote it as "P2: RDB2".
Thank you for the help.

Mehran September 27, 2018

@Kellan RDB2 stands for "reflexes disappear by age of two months".

The stimulus tell us that "this three-month-old baby exhibits these reflexes" or stated another way, these reflexes did NOT disappear by the age of two months.

This means not RDB2 so this is why I wrote P2 that way.

Hope that helps! Please let us know if you have any other questions.