Very informative. Thank you.
By the way, I bet you hear 'keep someone updated with what's going on in the world' more often than ' keep someone up-to-date with what's going on in the world', right? Do we actually say 'keep xx up-to-date'?
***** NOT A TEACHER *****
Hello again.
(1) Until someone else answers, let me try.
(2) Your question sent me to three good dictionaries.
(3) I discovered something that I had completely overlooked:
update = a verb
up to date/ up to date = an adjective.
(4) Here are some examples from the dictionaries (I may have changed them a bit):
An up-to-date hospital. = modifies "hospital"
The book will keep you up to date. = modifies "you."
*****
The magazine article will update you on the situation. = verb.
They need to update that book. = verb.
The TV reporter promised to keep the viewers updated. = past participle used as an adjective??? Modifies "the viewers"?
*****
Maybe (a BIG "maybe"), your two sentences mean the same:
I will keep you updated.
I will keep you up to date. (But in writing, definitely (?) NO hyphens in this case.)
Let's see what others say. Please post a similar question if no one else answers. I, too, want to know.
Have a nice day!