ものと思う states a belief or expectation the speaker takes as settled: "I fully expect that…", "I am confident that…". It goes after the plain form of a verb or an い-adjective; a な-adjective takes and a noun takes .
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I am confident that he will see it through.
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I expect this plan to go smoothly.
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I firmly believe that if you make the effort, you will succeed.
ものと思う or と思う
gives an opinion. ものと思う treats the content as the natural course of things, so it sounds more certain and more formal. You meet it in speeches, reports and business writing; in conversation
or
does the job.
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I think it will be sunny tomorrow.
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I expect the lives of citizens to improve from here on.
Usage notes
These go beyond a belief held now.
ものと思っていた
In the past, the expectation usually turned out wrong: "I had taken it for granted that…".
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I had assumed that permission would be granted as a matter of course.
、。
I thought he had already quit, but he was still working.
ものと思われる
The passive removes the speaker: "it is expected that". It is the form of news reports and official writing.
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Sales are expected to recover next fiscal year.