とされている means "is considered", "is regarded as": the view is generally accepted, and it is not the speaker's own. It is the quotation , (the passive of ) and , and follows a plain-form clause or a noun, with or without .
。
This temple is considered the oldest in Japan.
。
Sleep is regarded as very important for health.
。
That medicine is said to work.
It is the language of news, textbooks and formal speech. Because the claim is the consensus, the speaker does not vouch for it. In conversation does the same job.
。
They say vegetables are good for you.
Past views
reports what was believed then, and usually sets up a change.
、。
It used to be considered safe, but it is now known to be dangerous.
。
Cats were held to be sacred in ancient Egypt.
says the view has held for a long time and may still hold.
。
This painting has long been regarded as a work by Van Gogh.
とされている or と思われている
reports how people see something, an impression. とされている reports an established or official position.
。
People think he is a cold person.
。
She is regarded as the leading authority in this field.
Lingaku