Humankind would not have survived, as it clearly has, if our ancestors had not been motivated by the desire to sacrif...

Facundo on August 24, 2015

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Please explain answer

2 Replies

Melody on September 3, 2015

Let's diagram!

"if our ancestors had not been motivated by the desire to sacrifice themselves when doing so would ensure the survival of their children or other close relatives, then humankind would not have survived."

P1: not MDS ==> not HS
HS ==> MDS

We are also told that this kind of sacrifice, i.e. "MDS," is a form of altruism.

P2: MDS ==> A
not A ==> not MDS

We know that humankind has clearly survived

P3: "HS"

It follows that our ancestors were at least partially altruistic

C: A

So we are given a principle rule. We know that the contrapositive of this rule is triggered because we have "HS," so we can connect the contrapositive of P1 to P2 like so: HS ==> MDS ==> A to conclude A. Therefore, we have a valid contrapositive transitive argument.

Answer choice (A) has the same exact pattern of reasoning.

"Students do not raise their grades if they do not increase the amount of time they spend studying."

P1: not IAS ==> not SRG
SRG ==> IAS

"Increased study time requires good time management."

P2: IAS ==> GTM
not GTM ==> not IAS

"some students do raise their grades."

P3: SRG

"So some students manage their time well."

C: GTM

Just as in the passage, we are given a principle rule. We know that the contrapositive of the rule is triggered because we have "SRG." SO we can connect the contrapositive of P1 to P2 like so: SRG ==> IAS ==> GTM to conclude "GTM." So, just like the argument in the passage, we have a valid contrapositive transitive argument.

Hope that clears things up! Please let us know if you have any other questions.

on September 24 at 10:26PM

What is throwing me off with answer A is we appear to have "some" statements within the context of the answer choice and the way it is diagrammed is just like a normal S & N statement, and then we have a quantifier in the conclusion as well it seems (which is the same as the stimulus) but how is that similar if you have, in your diagram above P3: SRG when its a some statement and not a complete S & N statement? I just don't see how that's similar because you only have one quantifier statement in the stimulus and you have two in the correct answer choice.