These six words help you express possibility or confidence. They do not form a precise probability scale: context and tone matter, and several overlap.
- Maybe is a common, neutral way to say that something is possible but uncertain. Maybe the café is still open. It is especially common in everyday conversation.
- Perhaps usually means the same thing, but can sound slightly more formal or tentative. Perhaps we should ask for directions. It can make a suggestion feel less direct.
- Possibly also expresses possibility without saying that something is likely. The repairs could possibly take a week. It often works naturally with could or might, though it can also stand alone as an answer.
- Conceivably means that something is imaginable or possible, even if it seems unlikely. One missing file could conceivably delay the whole project. It often sounds more formal and emphasizes considering a possibility.
- Probably means that you think something is likely, while allowing room for doubt. Ravi will probably arrive before noon. You expect this outcome rather than merely considering it possible.
- Definitely expresses certainty or a firm commitment. I will definitely send the form today. It presents the speaker as sure; it does not independently prove that a statement is true.
Compare: Maybe I can help leaves the question open. I can probably help suggests that help is likely. I can definitely help gives a firm assurance. Choose according to your confidence, then consider how formal or tentative you want to sound.