I'm not so sure; I can't say for certain
Used when the speaker cannot assert something with confidence or finality. Often implies a degree of uncertainty or reservation.
I can't say for sure whether he will come.
I'm not so sure that's correct.
Standard kanji spelling for this expression.
Mixed kanji-kana spelling, common in casual writing.
Negative potential form of 言い切る (to declare, to assert), literally 'cannot say decisively'.