So - that - very
Very and so; so... that...
In academic English, do not use
so when you mean very. "Shakespeare was so good at characters" is not a good academic sentence. (It's o.k. when students, or their parents, are speaking less formally.) Don't use o.k. either. Nor should you use abbreviated forms of words like don't.
It is acceptable to use so in sentences where you are going to continue with a 'that' Clause - the consequence of the cause you have mentioned. "The French were so terribly affected by the winter that they retreated from Russia." But do not use so by itself, instead of very.
Do not use
that when you mean so. "He was that worried that he began chewing his nails" is bad academic English. (It is quite common in spoken English, particularly in the North of England.)
The reason for this confusion may be that the usual construction in formal English is "He was so worried that he began chewing his nails."