Consider the sentence, "prope virum summae virtutis sto." What case is virtutis and why?
I'm pretty sure that it is genitive due to description, but I'm not sure. In case it helps, I translated it as, "I stood near the man with the most courage."
Latin Language Stack Exchange is a question and answer site for linguists, teachers, and students wanting to discuss the finer points of the Latin language. It only takes a minute to sign up.Sign up to join this community
It is indeed genitive. First, no other form of virtus looks like virtutis. For that reason alone, it has to be genitive.
But what is the genitive doing in the sentence? The virtus comes with the adjective summa. Virtus can have many meanings, and "courage" is indeed a possible translation. Together summa virtus means "highest courage". Therefore vir summae virtutis means "a man of the highest courage".
While this translation is possible in English, it often most natural to translate with an adjective: "a very courageous man". Your translation "with the most courage" is possible as well. It should be noted that the superlative here is probably absolute; it does not express comparison ("most courageous of all") but just extent ("very courageous").
This Latin construction of using the genitive to express quality is known as genetivus qualitatis (the qualitative genitive). The ablative can be used similarly.
Finally, let me remark that sto is present tense. I would translate the sentence to English as "I stand near a very courageous man". However, this is not the correct translation — there are several ways to go about this translation task.