かも知れない

Use it to say something is possible, without assigning a precise probability. It is generally weaker than だろう/でしょう and much weaker than に違ちがいない. In the present, na-adjectives and nouns attach directly with no だ (静しずかかもしれない, 雨あめかもしれない). Their past and negative forms are 静しずかだったかもしれない and 雨あめではないかもしれない. The past is normally shown before かも (行いったかもしれない). かもしれなかった is also grammatical, but it suggests a possibility that did not materialize or is no longer relevant. Use かもしれません in polite speech and かも in casual speech. It is normally written in kana; 知しれない is rarely written in kanji.