posted by John on .
1. I am writing up today's diary.
2. I am keeping today's diary.
3. I am writing down today's diary.
4. I am writing today's diary.
Which expressions are correct?
To make #s 1, 3, and 4 correct, you'd have to add the word "entry" after the word "diary."
The expression is that you "keep a diary" -- or you "write a diary entry" or "write an entry in your diary."