N1
ものと思う
ものとおもう
Think that, Believe that, Expect that, Have confidence that, Absolutely
外国人観光客は日本語が話せないものと思っていたが、実際そうでもなかった。
I was under the impression that foreign tourists could not speak Japanese, but this was not the case.
Explanation
「ものと思う」 has 2 uses
1I trust that
A more formal "I think", with the confidence that things will normally turn out this way. In business you often hear ものと思われます.
この商品の品質でご満足いただけるものと思います。
I am confident that you will be satisfied with the quality of the product.
「可児江さんを支配人にすれば、このテーマパークは必ず成功するものと思います。」
'I think that if we make Mr. Kanie the manager, the theme park will surely be successful.'
2I had assumed
ものと思っていた looks back on an assumption: you took it for granted, but it wasn't so. Often followed by が or のに.
日本で最も寒い月は12月であるものと思っている人が多いが、実は2月だ。
Many people think that the coldest month in Japan is December, but actually it is February.
あの人はなんでもできると自信ありげに言っていたんで、仕事ができるものと思っていたが全然だった。
He said confidently that he could do anything, so I expected him to be capable of doing the job, but he was not at all.