Serious individual art collectors are usually discreet when making significant purchases or sales related to their collections. At art auctions, for example, these collectors often place anonymous bids for major artwork. Therefore, the whereabouts of most of the world's most valuable artwork is probably unknown.

Each of the following, if true, would weaken the conclusion above EXCEPT:

The value of a piece of art is purely subjective.

Serious art collectors usually publicize their new artwork several months after making a purchase.

Museums own the vast majority of the world's most valuable artwork.

Of all the individuals in the world who own extremely valuable artwork, only a few are considered serious art collectors.

The private collections of most serious individual art collectors are often displayed in public settings.

The Answer is A. However, I contend that A can't be right because if the value of art is subjective, then you can't know what art is valuable and not, therefore most of the valuable art is unknown (bc there is no agreed upon value!).

Where am I going wrong?

Thanks - Wilder

The conclusion is about the location of the artwork and not the price. So, A is kind of irrelevant.

first question of interest: if you contend that choice a is wrong, then which choice do you contend is right, and why?

remember that process of elimination is golden. choice a is sort of strange (discussed below), but it's the only choice that doesn't directly weaken the argument, and as such should be picked.

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i agree with you that choice a is weird. it doesn't directly weaken the logic of the argument, though.
rather, i guess (and i gather you, also, are saying) that it causes the argument to equivocate: if it is accepted as a premise, then the argument is at once talking about 'valuable' artwork and claiming that said 'value' is in the eye of the beholder. i agree that this is a problem: exposing equivocation in an argument doesn't, strictly speaking, weaken the line of argument, but it does cast doubt on the validity of the argument (in a reductio ad absurdum sort of way). i will bring this problem to the attention of those who are in charge of our can exams.

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if you are convinced that another of the answer choices is better than choice a, then post which one(s) you think is/are better.