What it means
と思う expresses the speaker's opinion, belief, or expectation about the statement before it. It is commonly translated as “I think that” or “I believe that.” The preceding clause normally uses a plain form, and its tense or polarity shows what the speaker believes, such as “will go,” “went,” or “will not go.” The expression can sound less direct than stating a fact because it presents the statement as the speaker's judgment.
Usage note
Before と思う, nouns and na-adjectives normally require だ, as in 医者だと思う and 静かだと思う. In polite speech, use と思います; the clause before it usually remains in plain form, so 来ると思います is natural.
How to use it
彼は医者だと思います。
I think he is a doctor.
あの店は静かだと思います。
I think that shop is quiet.
この問題は難しいと思います。
I think this problem is difficult.
来週、妹は京都へ行くと思います。
I think my younger sister will go to Kyoto next week.
彼は医者だと思う。
I think he is a doctor.
あの店は静かだと思う。
I think that shop is quiet.
この問題は難しいと思う。
I think this problem is difficult.
来週、妹は京都へ行くと思う。
I think my younger sister will go to Kyoto next week.