He is feigning ignorance about that problem.

In order to understand his feelings, I had a deep conversation with him.

God only knows what he is thinking.

He is working hard to make his abilities known to the world.

I have no way of knowing what he is thinking.

He knows that pain through his own experience.

Learning about the ancient special kana usage is very important for understanding ancient Japanese.

The Jōdai Tokushu Kanazukai is one of the notation methods of ancient Japan.

The special theory of relativity is a theory proposed by Einstein.

She described the pain of a broken heart as tears.