* Skill or technique: In this case, "craft," "expertise," or "mastery" might be suitable.
* Art or creative activity: "Art," "creativity," or "expression" could be used.
* Formal discipline or branch of learning: "Field," "discipline," or "subject" might work here.
The best modern word to use depends on the specific context in which you are using "ars." For example:
* "The ars of persuasion" could be translated as "The craft of persuasion" or "The art of persuasion."
* "The ars of medicine" could be translated as "The field of medicine" or "The discipline of medicine."
Ultimately, choosing the best modern word requires understanding the specific nuance of "ars" in the context of your sentence.