Further evidence bearing on Jamison's activities must have come to light. On the basis of previously available eviden...

on March 11 at 11:46AM

Why is A incorrect as it invokes the S to conclude N just like stimulus

Hi could you please explain why A is incorrect? The way it was explained in the previous post really was not too clear

1 Reply

on March 11 at 05:50PM

Hello @amf,

Good question! Answer choice A is a valid argument with sufficient and necessary reasoning. However, you have to look a bit closer to see why it does not most closely parallel the argument.

On the basis of previous evidence alone (PEA), it would have been impossible to prove that Jamison was guilty (IPG).

PEA - -> IPG

However, Jamison has been proven guilty. (In other words, not impossible to prove guilt: not IPG)

This leads to a contrapositive of our first diagram.
not IPG - -> not PEA

"Not previous evidence alone" is our conclusion. We did not simply invoke sufficient to conclude necessary. Rather, the necessary condition was negated, from which we conclude that the sufficient did not occur.
not N - -> not S

There was no negation involved in answer choice A. It did not conclude that the sufficient condition did not occur.

If someone is on the old list (OL), that person could not have purchased the property within the last year (not PWY).
OL - -> not PWY

In order for this to match the stimulus, the premise would have to be:
Jamison purchased his house within the last year (PWY).

PWY - -> not OL

Therefore he is not on the old list.

Does that make sense?