The AをBと + verb (verb + A as B) construction can be made into the passive form like so:
- [non-passive] 山田氏を学者だと思う。
(I) regard Mr. Yamada as a scholar.
- [(direct) passive] 山田氏は学者だと思われる。
Mr. Yamada will be regarded (by someone) as a scholar.
- [indirect passive] (私は)山田氏を学者だと思われる。
I will have Mr. Yamada (incorrectly) regarded as a scholar.
- [relativize 2/3] 学者だと思われる山田氏
Mr. Yamada, who will be (incorrectly) regarded as a scholar
I added "will" in some of the corresponding English translations because you need to use 思われている when it's about something at present and the subject of "think" is a third person.
Since these are still AをBと, だ can be safely dropped:
- [non-passive] 山田氏を学者と思う。
(I) regard Mr. Yamada as a scholar.
- [(direct) passive] 山田氏は学者と思われる。
Mr. Yamada will be regarded (by someone) as a scholar.
- [indirect passive] (私は)山田氏を学者と思われる。
I will have Mr. Yamada (incorrectly) regarded as a scholar.
- [relativize 6/7] 学者と思われる山田氏
Mr. Yamada, who will be (incorrectly) regarded as a scholar
Sentence 3 and 7 are indirect passive sentences (unambiguously). However, Sentences 2, 4, 6 and 8 are usually not interpreted as above when there is no context. Instead, this type of 思われる is taken as spontaneous-れる by default:
- 山田氏は学者だと思われる。
[spontaneous] I (spontaneously) think that Mr. Yamada is a scholar. / It appears that Mr. Yamada is a scholar.
Note that this sentence no longer has anything to do with passive voice even though it has れる. This れる just adds the mood of spontaneously (or somehow, vaguely, etc.)
Applying the rules of relative clauses, you can construct these noun phrases:
- 学者(だ)と思われる山田氏
[from 2/6] Mr. Yamada, who will be (incorrectly) thought of as a scholar
- 学者だと思われる山田氏
[from 9] Mr. Yamada, who appears to be a scholar
These look the same, but 11 is the default interpretation. The interpretation like 10 is not unnatural, but there needs to be a context such as that Mr. Yamada is clearly annoyed by being mistaken for a scholar.
Prescriptively speaking, when 11 is intended, だ should not be dropped. This is because it's from 山田氏は学者だ, which is a sentence. So this 学者だ is still a sentence, just like 大丈夫だ in 大丈夫(だ)と思います is a sentence. But I somehow feel it's safe to drop this だ in a very short case like this.
You can apply the same discussion with 彼が立派に思われる. Technically, it can mean both "He is going to be (incorrectly) thought of as being respectable" (passive) and "I feel he is respectable" (spontaneous). But for the former to make sense, you need some rare context where being thought of as a respectable person is undesirable to the speaker for some reason.
Fortunately, thanks to this rule, you will see 思われている (not 思われる) when the passive voice is intended and the sentence is not about something in the future. Compare:
- 学者だと思われる山田氏
Mr. Yamada, who appears to be a scholar
- 学者(だ)と思われている山田氏
Mr. Yamada, who is (incorrectly) thought of as a scholar
Therefore, the rule of thumb is that when you see 思われる (and 感じられる, 考えられる) for something not in the future, you can say it's spontaneous (or honorific). Also note that something like 認める is always an intentional action, so 認められる does not allow a "spontaneous" interpretation.
To make it easier for people with better knowledge in Japanese than us, while I'm not saying that the questions here need to be ones where one can answer "YES" or "NO", at least I didn't at first understand what you wanted to ask.
– Tuomo May 13 '23 at 14:16