One is likely to feel comfortable approaching a stranger if the stranger is of one's approximate age. Therefore, long...

Sydneh on May 20, 2016

Please explain

Why is the correct answer E? And in general with Errors of reasoning questions, what is a good indicator to know that the author has overlooked another possible situation? Thank you!

2 Replies

Mehran on May 21, 2016

@sydbrown6 let's take a look.

This stimulus is an argument that can be broken down as follows:

P1: One is likely to feel comfortable approaching a stranger if the stranger is of one's approximate age.

We know "if" introduces sufficient so we can actually diagram P1 as follows:

OAA ➡️ FCAS
not FCAS ➡️ not OAA

P2: Most long-term friendships begin because someone felt comfortable approaching a stranger.

This is a quantifier that we can write out as follows:

LTF-most-FCAS

C: Long-term friends are probably of the same approximate age as each other.

This is also a quantifier that the author is attempting to create by combining P1 and P2.

The problem here is that the variable P1 & P2 share in common is FCAS (i.e. felt comfortable approaching stranger), but FCAS is our necessary condition in P1 so we cannot make a valid deduction here.

The author is assuming that P1 actually says FCAS ➡️ OAA (contrapositive not OAA ➡️ not FCAS).

The author is overlooking the possibility (i.e. failing to address) that a person who might not be a stranger's approximate age would nevertheless feel comfortable approaching that stranger.

Notice that according to P1, this is entirely possible because not OAA is negating the sufficient condition and we know that the negation of the sufficient condition tells us nothing (i.e. don't just negate!).

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

Sydneh on May 22, 2016

Thank you!