Adverb
(idiomatic) Without doubt.
I know this for a fact.
Synonym: for a certainty
Used other than figuratively or idiomatically: see for, a, fact.
The doctor had asked for a fact that I could not remember.
I know for a fact that this idea of the Jews causing the war and the Jews being so all important is nonsense. But that was Hitler's idea, and...was pure fantasy. As I say, Hitler is a riddle to me and will always remain so. Joachim von Ribbentrop
There was a huge, tremendous amount of disabled veterans and the Veteran's Administration just wasn't geared up for it. I know for a fact that it's getting better and better. R. Lee Ermey
All problems are unsolvable. The essence of the existence of a problem is that there is no solution. Looking for a fact means there is no fact. To think is not to know how to be. Fernando Pessoa
I'm always in my pajamas, unless I know for a fact that people are taking my picture. Bethenny Frankel
Be careful what you wish for. I know that for a fact. Wishes are brutal, unforgiving things. They burn your tongue the moment they're spoken and you can never take them back. Alice Hoffman
Then shut up or grab a sword and come help. (Takeshi) Is that a challenge? (Savitar) It would be if I didn't know for a fact that you're too lazy to rise to one. (Takeshi) Sherrilyn Kenyon