So，I've recently seen the term 以及 used a number of times in written text. For example, in a short story by 叮咛 I read " 这位总统为国家、政府以及人民贡献了所有的力量，人们很尊敬他。". Another chinese stack exchange answer asked about the difference between it, 和， and 与 What is the difference in use between 以及, 和 and 与? － but， I‘m wasn't entirely satisfied by the answer. One said that 以及 only connects phrases (but that doesn't seem true in the above example). And if it is true, how is it different from say "还有“ ？
谢谢大家！
I think the primary difference is formality.
以及 sounds formal. It is rarely used in spoken language but acceptable, okay in casual writing and common in formal writing.
还有 sounds very colloquial. It's fine in casual writing but should be avoided in formal writing.
It's not true to say 以及 only connects phrases. A quick search will give you many good counter-examples. However when it comes to connecting phrases, 以及 does a better job than the other choices. That's exactly where people would use it in colloquial language - connecting short words with 以及 sounds too formal but connecting long words or phrases sounds okay.
还有 sometimes (not always) gives the listener an impression, or means, that you forgot to mention something before and suddenly you remembered it, or that you don't think those are important. But in most situations, it's just a matter of formality.
