The title is a quote from this answer:
Stack exchange is not the place to learn first order logic, buy a book by Quine.
Depending on the interpretation of this quote, it may even contain a grain of truth. I certainly think that stackexchange is a good place to ask questions when you have specific problems while learning first order logic. However, different texts on first order logic use different conventions and different names, so questions of first order logic might have different answers, depending on the books used by the questioner.
The question which provoked the answer from which I took the quote has many answers, but most of these answers contradict the books from which I learned first order logic. However, these books were mathematical books written in German, so I don't want to exclude the possibility that philosophical books written in English really use completely different conventions with respect to that question.