There is no hard and fast rule. The rule I prefer is "if you pronounce the 's', then spell it". I would say Brutuses, so I would write it as Brutus's.
Interested in Language
Hi, I came across a problem when writing my essay. Do you say: Brutus's friend or Brutus' friend? (meaning - Brutus has a friend)I googled both possibilities. Is there a rule for adding ' or 's with names?
Thank you for your help.
I agree with Mike. That's how most BrE speakers say and write it, too.