The pronoun ‘it’ can be used where the subject is unclear at C1, and verbs such as ‘conclude’ are only used by C1 learners. For example:
It was concluded that it never existed.
However, this post is about reporting with modal verbs.
C1 point 208 in MODALITY is defined as:
‘can’ in passive reporting clauses in a more formal impersonal style (e.g. for reports and academic contexts), such as ‘It can be said that’, ‘It can be argued (that)’, ‘It can be concluded that’, ‘It can be considered”
*Also see C1 point using dummy subjects.
This is similar to the B2 English Vocabulary Profile point: ‘BE + said to’ which means
many people believe something about something
Drinking plenty of water is said to be good for your skin.
Also, the modal + passive form in a range of contexts is also B2, or is the following example impersonal enough to be C1?
I think that the best that can be said about this is…
*’could’ should also be accepted under this point as C1 complexity. For example:
It could be argued though that the only thing that motivates men is chasing women.
I think that it could be considered in the best interest of the United States that Abel stay alive.
A search in iWeb for:
It_P can be argued|said|argued|concluded|considered
1 IT CAN BE SAID 5184
*The following example is not really ‘impersonal’ knowledge.
I‘m not a biologist, so everything I know about it can be said in one minute.
2 IT CAN BE ARGUED 4337
3 IT CAN BE CONSIDERED 2497
4 IT CAN BE CONCLUDED 1300