In Michael Swan's "Practical English Usage", he states in section 16.1:
Many verbs besides auxiliaries can be followed by forms of other verbs (or by structures including other verbs). This can happen, for example, if we talk about our attitude to an action: the first verb describes the attitude and the second refers to the action. The second verb structure is often rather like the direct object of the first verb.
Additionally he gives the following examples:
I hope to see you soon.
I enjoy playing cards.
I saw that she was crying.
What confuses me is the part "rather like the direct object".
If I'm not mistaken
the non-finite clause "to see you soon" is the object of the verb "hope"
the non-finite clause "playing cards" is the object of the verb "enjoy".
the nominal clause "that she was crying" is the object of the verb "saw".
Why does Swan consider those structures as "rather like direct objects" instead of "direct objects"? Do grammarians use other terms for those structures or is it possible that Swan uses the term "direct object" only for noun phrases, but not for finite/non-finite clauses?
I have checked how the term "object" is defined in "A Comprehensive Grammar of the English Language" by Quirk, Svartvik and Leech:
10.7 Object: direct and indirect
Like the subject, the object is normally a noun phrase or a nominal clause.
15.3 Nominal clauses
Nominal claues (clauses approximating in function to noun phrases) fall into six major categories:
to-infinitive clauses (15.10 f)
-ing clauses (15.12 ff)
Nominal that-clauses may function as:
direct object: I noticed that he spoke English with an Australian accent.
15.10 To-infinitive clauses:
Nominal to-infinitive clauses may function as:
direct object: He likes to relax.
15.12 -ing clauses:
Nominal -ing clauses may function as:
direct object: He enjoys playing practical jokes.