What's the difference between [今日は] ＆ [ こんにちは ] ？ I asked this question because two natives gave me a mark on this word of my note. I have no idea what's wrong with it. I thought most my teachers in university told me that 今日は is the kanji version of こんにちは. Then I have no idea why it couldn't be written like if I referred to the correction of native speakers. What's the actual meaning of it? If maybe something that I don't know that two of them have different usage for certain situations. (P.S. my note also has been corrected by my teacher and she didn't give me any mark on this word, unlike natives who corrected it). P.S. the word I use is for for a greeting purpose.