The three words which I was thinking of were 本当, 確か, and 絶対, but I'm sure there are more. How do these words differ from each other? The dictionary defines these three words fairly similarly but could someone explain the nuance and correct usage of each, as well as other words which can mean 'true/certain'?
本当 real, true 確か certain 絶対 absolute
- 彼は本当に知らない。(He really does not know.)
- 彼は確かに知らない。(He certainly does not know.)
- 彼は確かには知らない。(He does not know for sure. He has some vague idea, but does not understand it completely.)
- 彼は絶対(に)知らない。(He absolutely does not know. I am absolutely sure that he does not know.)