In addition to the labor and materials used to make wine, the reputation of the vineyard where the grapes originate p...

Irina on September 30, 2019

@ksosen13,

Let's look at the structure of the argument.
We are given the following premises:

Labor and materials determine the price of the wine.
Reputation of the vineyard determine the price of the wine.

And conclude that:
Therefore, an expensive wine is not always a good wine.

Let's look at (C) and (D):

(C) The reputation of the vineyard does not always indicate the quality of the wines.

If we negate this assumption - the reputation of the vineyard always indicates the quality, meaning better reputation -> higher price -> better quality, the conclusion will no longer makes sense as reputation will always indicate the quality. Thus, we can conclude that this is a necessary assumption for the argument to follow logically, only if there is not always a direct correlation between the reputation -> price- > quality, could we conclude that more expensive wine is not always a good quality wine.

(D) The reputation of the vineyard generally plays a greater role in determining the price than other factors.

This assumption has no impact on the conclusion, if we negate it, and the quality of the grapes or labor plays a greater role in determining the price, we could still conclude that more expensive wine is not always a good wine because the reputation would still play a role - even though a comparatively smaller one - in determining the price.