I'm having a hard time trying to figure out how these infinitive phrases function (if they are infinitive phrases at all) in the following examples. I have learnt that they can act as nouns, adjectives and adverbs.
Firstly,
It was impossible to understand him.
You were clever to find the answers so quickly.
You don't look happy to see me.
Then, it occurs to me that what we are modifying are adjectives, and adverbs can modify adjectives. In these previous cases, would the phrases be functioning as an adverb?
Secondly,
It’s difficult for us to hear what she’s saying.
In this last example, is it acting as a direct object?
What's difficult? To hear what she's saying.
Or it might be a subject complement.
To hear what she’s saying is impossible for us.
If so, would it be functioning as a noun?
All the previous examples feature linking verbs as the main verbs.
Finally, in these following sentences, with abstract nouns and indefinite pronouns (and action verbs), it may be easier to see the adjectival quality:
I had no one to talk to.
When I’m travelling, I always take something to read.
I would really appreciate any insight about this. Thank you.
Edit: I have found a website that explains in detail adjectives. It presents the to-infinitive as a way of complementation. It does not specify whether it's as a noun, and averb or another adjective.
Many predicative adjectives can be followed by the to-infinitive. Examples of the form will suffice here:
The hotel was hard to find
They were thrilled to discover how much
They are certain to go
He was quick to respond
Again, a few adjectives actually require complementation by a to-infinitive. For example:
The machine is inclined to be noisy
She is bound to come to your party
She is able to come
