From The Chicago Manual of Style website:
Shop Talk: A favorite debate in the CMOS community is whether new word usages should be allowed, with classic examples of hopefully and literally. How do you think we should draw the line between common usage and Standard Written English? Are there cultural or academic checkpoints that a word must go through before making the transition?
Ben: The first thing to recognize is that what we think of as “new” usage is very often not that new at all, thanks to what Stanford linguist Arnold Zwicky has called The Recency Illusion. We tend to think of stigmatized language patterns as artifacts of our current age, when in fact they can reflect long-standing usage among established, respected writers. But just because you can find Alexander Pope writing “Every day with me is literally another yesterday for it is exactly the same” in 1708, that’s not going to assuage those who insist that literally should only be used, well, literally, rather than emphatically or hyperbolically. I often point to such historical evidence in usage disputes, but I doubt that I’m convincing anyone who has already decided that a particular point of usage is simply wrong.
I chalk up much of this black-and-white thinking about language to pedagogy: in our schooling, we are constantly encouraged to think that there is only one right answer, which flies in the face of the flexibility and mutability of language. And so as adults, we look to authoritative texts like usage manuals and dictionaries to uphold an unequivocal standard. The messy linguistic facts reveal that there is no single standard, however, even if we limit ourselves to a supposedly unitary “Standard Written English.” Different social contexts require subtle adjustments to our language use, and for the most part we navigate these changes of register without even consciously thinking about it. It’s only when we get snagged on a shibboleth like literally or hopefully that questions of propriety arise and we expect an authority to decree that there is One Right Way.
Good usage manuals and dictionaries won’t shy away from the complexity of language but will instead offer advice about what is typically expected in different written and oral styles.