The druid stones discovered in Ireland are very, very old. But this particular druid stone was discovered in Scotland...

Naz January 14, 2015

The conclusion of the argument is: "it (this particular druid stone) must be of more recent vintage."

Why? "The druid stones discovered in Ireland are very, very old." We are told, however, "this particular druid stone was discovered in Scotland."

So we can diagram the first sentence:

P1: DSI ==> VVO
not VVO ==> not DSI

We diagram the second sentence:

P2: not DSI

We diagram it like this because we are told that this particular druid stone is from Scotland, not from Ireland. So, to keep our conditions consistent, we will say this druid stone is "not from Ireland."

And we conclude:

C: not VVO

Again, we are trying to keep the conditions consistent, so being of a "more recent vintage," is the same as not being "very, very old."

So, what's the flaw here? We are mistaking a necessary condition for a sufficient condition. We can never infer anything else from a necessary condition. Thus, since "not DSI" is a necessary condition, we cannot infer "not VVO," which is a sufficient condition.

Remember, we must always reverse AND negate to come up with a correct contrapositive. Here, we have not reversed.

It's also important to note that the necessary conditions of a principle rule and its contrapositive, in this case: "VVO" and "not DSI," can act as a viable option. So, that means we could have druid stones that are not from Ireland, i.e. from Scotland, that are very, very old.

We have been given no information restricting us to believe that THE ONLY "very, very old" druid stones are from Ireland. "Very, very old" druid stones can be from other places, as well, because we have not been given any such restrictions in our argument.

Thus, answer choice (E) is our answer because it describes this very issue: "takes the fact that all members of a group have a certain property," i.e. that all druid stones from Ireland are very, very old, "to constitute evidence that the members of the group are the only things with that property," i.e. that any druid stones not from Ireland (example: Scotland) cannot be as old.

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

yababio May 21, 2015

Theres no video for this question

Naz May 21, 2015

There is no need for a video explanation to this question since it has no visual components. Please refer to the written explanation above for a breakdown of the problem.

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

ariella February 26, 2017

Why is B incorrect?

Mehran February 27, 2017

@ariella (B) is wrong because the argument is not taking "most" and applying it to all.

Notice it does not say that "most druid stones discovered in Ireland are very, very old."

Rather it is saying that all druid stones discovered in Ireland are very, very old.

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

niki-dowlatshahi September 29, 2018

Great explanation on this one! Well done Melody.
Sometimes its more comprehensive to read the explanation, step by step.
thanks.

Gozi November 12, 2019

Great explanation by Naz! It clicked for me!

Karen-Norris May 6, 2021

So would the conclusion have been correct if the first sentence said, "Only Irish Druid Stones are very, very old."?