Some visitors to the park engage in practices that seriously harm the animals. Surely, no one who knew that these pra...

Victoria on May 4, 2021

Hi @naj2,

Happy to help!

Let's start by diagramming the stimulus.

Premise: "Some visitors to the park engage in practices that seriously harm the animals."

Visitors - some - Engage in harmful practices

Premise: "Surely, no one who knew that these practices seriously harm the animals would engage in them." In other words, if people knew that the practices were harmful, then they would not engage in them.

Know practices harmful --> Not engage in harmful practices
Engage in harmful practices --> Not know practices are harmful

Remember that we can connect an S&N diagram with a quantifiers diagram as long as we have the sufficient condition in common and the arrow points away from the quantifier.

Visitors - some - Engage in harmful practices --> Not know practices are harmful

This gives us our conclusion: "some of the visitors do not know that these practices seriously harm the animals."

Visitors - some - Not know practices are harmful

So, what is the general structure of the stimulus?

P: A - some - B
P: B --> Not C
C: A - some - Not C

Answer choice (C) has the exact same structure.

Premise: "Some of the people polled live outside the city limits"

Polled - some - Live outside city limits

Premise: "However, no one who can vote in city elections lives outside the city." In other words, if you can vote in city elections, then you do not live outside the city.

Vote in election --> Not live outside city limits
Live outside city limits --> Not vote in election

Then we can conclude:

Polled - some - Live outside city limits --> Not vote in election
Polled - some - Not vote in election

In other words:

P: A - some - B
P: B --> Not C
C: A - some - Not C

Answer choice (B) is incorrect for a number of reasons.

Petition -some - Mayor's supporters

Petition --> Denounced
Not denounced --> Not petition

Therefore, there are two issues which make answer choice (B) incorrect:

(1) We need to reverse the some statement to draw our conclusion, a step not required by the stimulus.

(2) The second statement uses "all" rather than "none." This results in the conditional being directly applied i.e. we do not use the contrapositive.

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