Terminology: Definition of the term "direct object"

Question

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?

Edit:

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

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(a) FORM

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:

that-clauses (15.4)

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to-infinitive clauses (15.10 f)

-ing clauses (15.12 ff)

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15.4 That-clauses:

Nominal that-clauses may function as:

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direct object: I noticed that he spoke English with an Australian accent.

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15.10 To-infinitive clauses:

Nominal to-infinitive clauses may function as:

...

direct object: He likes to relax.

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15.12 -ing clauses:

Nominal -ing clauses may function as:

...

direct object: He enjoys playing practical jokes.

...

Answer 1

In comments, BillJ wrote:

A[s] far as your first two examples are concerned, the major alternative view is that such non-finite clause are not direct objects but catenative complements, where "hope" and enjoy" are catentive verbs and the clauses that follow them are catenative complements. This view hinges on the fact that they don't behave like objects. Your third example is different: the clause "that she was crying" is finite, so not catenative, though it is complement of "saw".

I haven't read Swan, but I suspect he uses the expression "rather like direct objects" because like objects, they are complements of the verbs that precede them. My advice to you is to take direct objects as consisting solely of noun phrases. There are one or two minor exceptions, but if you do that, you won't go far wrong.

Answer 2

In a comment, Edwin Ashworth wrote:

Swan has the grace to acknowledge that there are different opinions held by different grammarians hereabouts. Some people trot out the views of their favourite schools as if they were unassailable, often without even a reference. This would be unacceptable in a scientific paper. / You yourself don't arrogate here, but neither do you provide supporting evidence that some hold the view that 'the non-finite clause "to see you soon" is the object of the verb "hope" [in the example given]'. / That having been said, Professor Lawler's credentials make his answer at the earlier thread very significant....