There has been many times where I've seen writers use only one parenthesis, generally at the beginning of whatever they are saying, i.e. an open parenthesis, but not at the end. What is the context for using parentheses like this?
Are you sure you aren't missing the closing bracket? In philosophy is possible it closed in another paragraph. Especially in Kant/Hegel/heidegger or similarly dense reading.
I read lots of Phil and have never seen this. Would welcome a real example.
Sorry, I just thought of something, a dash can be considered a parenthesis and does not need to be closed. Are you reading some kind of translation? Maybe the translator took a weird style choice and changed dashes to brackets (unlikely.