说不定【shuōbudìng】

说不定 means "might well". It goes after the subject or at the start, and it raises a possibility the listener may not have thought of. It belongs to conversation.

Literally it is "can't say for certain", and it keeps that meaning as a predicate at the end of a sentence: the matter isn't settled yet.

As a reply, 那可说不定 means "you never know".

说不定 or 不一定

Both admit uncertainty, but they point in opposite directions. 说不定 suggests that something could happen; 不一定 doubts that it will.

Not a question

A 说不定 sentence is a statement. To ask whether something might happen, use 会不会.

• × 说不定他会来吗？ → 他会不会来？