EDIT: Although very similar, this isn't a duplicate of the thread linked by @binom. The linked thread deals with how 「ではなく」 is formed; this one, with the sense in which 「ではなく」 is used.
I read the following phrase in a Japanese forum, regarding whether to use "something" or "a thing/ things" in English.
自分が何の用事があるか分かっている場合は、「something」ではなく「a thing/ things」を使うべきでしょうか？
In my question title I changed the quoted parts of the sentence to 「x」 and 「y」 respectively, because the focal point of my question isn't about them, but the 「ではなく」 part.
I was wondering if my attempt at translating the sentence is correct?
Shouldn't (you) use "a thing/ things" instead of "something" if (more lit: in the event that) you know (what it is) you're doing?
That's the gist I get from it, despite not having come across 「ではなく」 used in this way. In my (admittedly limited) experience I thought the plain form 「じゃなくて」 would be used within the bulk of the sentence, as polite forms were usually reserved for the end? Furthermore, I expected a 「より...の方がいい」 construction to express preference. Obviously there's more than one way to say something, but this isn't one I've encountered until now.