Perhaps

…かもしれない

...kamo shirenai

(indicating a lack of certainty)

…でしょう

deshō

(indicating a lack of certainty)

ひょっとして

hyottoshite

(indicating a lack of certainty)

もしかして

moshikasite

(indicating a lack of certainty)

多分

tabun

(indicating a lack of certainty)

恐らく

osoraku

(indicating a lack of certainty)

若しや

moshiya

(indicating a lack of certainty)