What use of the genitive is primarily found in phrases such as "magna pars eōrum"?

The correct answer is the partitive genitive. This construction is used to indicate a part of a whole, which is evident in the phrase "magna pars eōrum," where "magna pars" translates to "a great part" and "eōrum" specifies whose part it is. The genitive here clarifies that the great part belongs to a larger group or whole, which is characteristic of the partitive use, as it highlights that we are discussing only a portion or segment of a larger entity.

This particular use of the genitive is essential for expressing relationships of quantity or portions. It directly connects with the context of discussing subsets or fractions of larger groups. In contrast, other forms of genitive, such as possession or description, would serve different grammatical or contextual purposes. Thus, recognizing this distinction helps clarify why "magna pars eōrum" fits the partitive structure so well.