Why do we write “cum marito eius” (cum + abl+ gen.) and not “cum marito ei” (cum + abl+ abl.)?

Question

Pline wrote this sentence: “Sunt mihi et cum marito eius Minicio Iusto, optimo viro, vetera iura; fuerunt et cum filio maxima, adeo quidem ut praetore 5 me ludis meis praesederit”. I don’t understand why we have “cum marito eius” (cum + abl+ gen.) and not “cum marito ei” (cum + abl+ abl.). Thank you.

Answer 1

I think there are two issues that would be helpful to clarify here:

1. ei is the dative (not the ablative) of the demonstrative pronoun is/ea/id. Since Latin does not have a third-person personal pronoun, this demonstrative pronoun is used to mean he/she/it.
2. The possessive adjective suus, -a, -um is only used reflexively. (See the first note under §145 of the linked grammar entry from Allen & Greenough.)

Thus, if you want to say his/her/its, there are two options in Latin:

• Use the adjective suus, -a, -um agreeing with the noun, if it refers back to the subject, e.g. pater amat filium suum = "the father loves his [own] son."
• Use the genitive pronoun eius, as a standalone, if it does not refer back to the subject, e.g. pater amat filium eius = "the father loves his [someone else's] son."

In short: there is no non-reflexive third-person possessive adjective.

In the third-person, this is a relatively fixed rule. You'll note that there are cases, like the first-person adjective meus, -a, -um and genitive pronoun mei, where there isn't the same reflexive vs. non-reflexive distinction. In such cases--as your instincts tell you here--Latin almost always prefers the adjective, not the genitive pronoun.