When you want to express that something will probably happen, but are not certain, you can use the word 多ta分bun.

A more formal word than 多ta分bun is おそらく. It is equivalent to 多ta分bun in its level of certainty, namely the thing it described is felt as probable but not certain.

When you have a higher degree of certainty, you can use きっと, which roughly translates to surely or definitely, and indicates a strong belief or expectation.

Another word that translates to surely or definitely is 確tasiかに. When using 確tasiかに, the speaker indicates that their belief is based on their knowledge, experience, or evidence. So while both words can be translated to certainly in English, きっと is more about expressing a strong expectation or belief, while 確かに is more about confirming or asserting a known fact. 確tasiかに is also often translated as indeed.

Finally, the word 必kanaraず can be used to express a very high level of certainty. It is equivalent to definitely or without fail.

Breakdown of osoraku sore ha tadasii kotae de ha arimasen.