I unwittingly wrote a new post over my first through the edit function. I've just deleted the new message, and re-written my question as close to what I wrote initially as possible.

[1] All his results were checked to decide whether we will hire him or not.

Grammatically, doesn't the author have to supply the sentence with the hidden subject "we" in the form of "for us" because the subjects are different?

Hiro/ Sendai, Japan

HSS

“Grammatically, doesn't the author have to supply the sentence with the hidden subject "we" in the form of "for us" because the subjects are different?”

No.  That 'rule' does not apply generally to all cases, but only to certain verbs.

I believe you are referring to something like this:  I waited to enter.  I waited for him to enter.

CJ

 Yes, it is clear from the sentence that "we" made a decision.
But it is not clear who checked the results. It could have been an external agency.

HSS

“ How would you tell the subject of a to-infinitive in a passive sentence like that?”

 

I think you mean the agent,  not the subject. The grammatical subject is the results.

But anyway, the point of using the passive is when "who did it" is either unimportant, not known, or deliberately omitted. If you think that it's important to say who did it, then don't use the passive. WE checked his results so we could hire him.

HSS

“How would you tell the subject of a to-infinitive in a passive sentence like that?”

With infinitives of purpose, it seems to me that both the agent of the passive and the subject of the infinitive are an indeterminate "somebody".  The two somebodies are usually but not necessarily coreferential.

Soft music is played to relax the patient.
Prices were reduced to attract more customers.
New laws were passed this year to keep the streets safe.
This medication has been used to treat depression in young adults.
All his results were checked to decide whether we will hire him or not.
The data is being analyzed to determine whether the concentration of carbon dioxide is increasing.

Rough paraphrases:

Somebody plays soft music because somebody wants to relax the patient.
Somebody reduced prices because somebody wanted to attract more customers.
Somebody passed new laws this year because somebody wanted to keep the streets safe.
Somebody has used this medication because somebody wanted to treat depression in young adults.
Somebody checked all his results because somebody wanted to decide whether we will hire him or not.
Somebody is analyzing the data because somebody wants to determine whether the concentration of carbon dioxide is increasing.

The infinitive is adverbial, telling why the action of the main clause was done.  These can be rephrased in various ways, the most usual being "for the purpose of ---ing".

Soft music is played for the purpose of relaxing the patient.
Prices were reduced for the purpose of attracting more customers.
New laws were passed for the purpose of keeping the streets safe.
This medication has been used for the purpose of treating depression in young adults.
All his results were checked for the purpose of deciding whether we will hire him or not.
The data is being analyzed for the purpose of determining whether the concentration of carbon dioxide is increasing.

In a strange way, the entire main clause is the subject of the infinitive.  Or, more precisely, the statement of the belief that underlies the whole sentence has the entire main clause as the subject.

[--- play soft music] relax patient       (The playing of soft music relaxes the patient.)
[--- reduce prices] attract more customers  (The reduction of prices attracts more customers.)
[--- pass new laws] keep streets safe     (And so on.)
[--- use this medication] treat depression ...
[--- check his results] decide [we hire ...]
[--- analyze data] determine [ concentration ... increase]
____

I haven't figured out yet why this works differently for the monkey, where a possible paraphrase is "so that ... can/could".

The monkey stood there so that he could take a picture.

However, in this case, we definitely do not have

[monkey stands there] takes a picture.

CJ