In "How soon is too soon to ~?", what is hidden/omitted after the subject 'how soon'?

"How soon is too soon to start kids on a computer?"

I think the grammatical role of 'how soon' is an adverb and the subject should be a noun. How can I understand this sentence grammatically?

Solution 1:

The subject of the sentence

[1] How soon is too soon to start kids on a computer?

is the interrogative phrase how soon. Although it is the subject, CGEL, at least, does not consider that phrase to be a noun phrase (NP). What is certain is that the subject need not invariably be an NP (see the discussion below). Within that interrogative phrase, the interrogative word how has the role of an adverbial degree modifier.

The sentence [1] is a single clause, whose type is an open interrogative clause. Here 'open' refers to the fact that the characteristic use of such clauses is to ask an open question, a question that has any number of possible answers. This is in contrast to a closed question such as Are you generous?, which has a closed set of answers (here just 'yes' or 'no').

Discussion

Although the role of the subject is usually played by an NP, that role can be played by other grammatical structures. Here are some examples from CGEL (p. 500):

(b) Subjects with the form of clauses or phrases of other categories than NP

We can extend the concept of simple agreement to cover constructions where the subject is a clause or some other kind of phrase than an NP. These are treated as 3rd person singular:

[6]   i  That he is trying to hide something is all too plain.          [declarative clause]
       ii  Why he resigned remains a mystery.                                      [interrogative clause]
      iii  Not informing the neighbours was a serious mistake.        [gerund-participial clause]
      iv  From here to London is over fifty miles.                                 [PP]
       v  Rather too big for your boots is what you are, my boy.    [AdjP]

The default category in the system of person is 3rd and, certainly for the purposes ofagreement, singular is the default number, so in the absence of any motivation for 1st or2nd person or for plural, subjects like those in [6] take 3rd person singular verbs.

In several places, CGEL gives examples of interrogative phrases playing the role of the subject. Here they are:

(b) Open interrogatives

Here inversion accompanies the placement in prenuclear position of a non-subject interrogative phrase. As with closed interrogatives, inversion is normally limited to main clauses:

[9]            SUBJECT + VERB ORDER                     SUBJECT-AUXILIARY INVERSION
        i  a.  Who told you that?                             b.  What did she tell you?
       ii  a.  And after that you went where?      b.  And where did you go after that?
      iii  a.  I wonder what she is doing.             b.  What is she doing?

In [ia] the interrogative phrase is itself subject: inversion occurs only after non-subjects, as in [ib].

                                                                                                                                                        (p. 96)

And here:

3.1 Distinctive grammatical properties of the subject

(f) Open interrogatives

The rules forming open interrogatives likewise distinguish sharply between subject and non-subject elements:

[5]   i  Who bought it?              [interrogative element as subject: basic order]
       ii  What did you buy?        [interrogative element as non-subject: inverted order]

If the interrogative element is subject, the order is the same as in the declarative(cf. Someone bought it), but if it is non-subject, then the interrogative element is usually placed in front position, triggering subject-auxiliary inversion.

                                                                                                                                                    (p. 238)

It is fairly clear why CGEL does not say that interrogative phrases are NPs.

First, typical NPs can function as subjects, predicative complements (PCs), and objects. But while interrogative phrases can function as the first two, they cannot function as objects.¹

^{1We've already seen examples where they function as subjects, and here is an example where an interrogative phrase functions as a PC: Two months is how soon. On the other hand, there are no known acceptable examples where an interrogative phrase serves as an object of a transitive verb.}

Second, interrogative phrases do not have the structure of an NP. An NP has as its head either a noun, or else a dependent that in ordinary NPs is adjacent to the head, usually a determiner or an internal modifier. The latter type of NP is called a fused head NP. For example, in Where are the sausages? Did you buy [some] yesterday?, the determiner some is the fused head. It can appear adjacent to the head noun in NPs such as some sausages. Similarly, in The first candidate performed well, but [the second) did not, the fused head is the modifier second. That modifier can appear next to the head noun in the second candidate. However, there is no NP whose head is a noun and in which how soon can appear adjacent to the head noun.

Types of clauses

Here is what CGEL says about what types of clauses there are in general (p. 95):

1 Type as a grammatical system of the clause

■ The five major categories

Clause type is the grammatical system whose five major terms are illustrated in:

[1]   i  You are generous.               [declarative]
       ii  Are you generous?              [closed interrogative]
      iii  How generous are you?     [open interrogative]
      iv  How generous you are!     [exclamative]
       v  Be generous.                       [imperative]

■ Characteristic use and general definitions

Each of the categories is associated with a characteristic use as follows:

[2]       CLAUSE TYPE           CHARACTERISTIC USE
         i  declarative                   statement
        ii  closed interrogative    closed question
       iii  open interrogative      open question
       iv  exclamative                 exclamatory statement
        v  imperative                   directive

A closed question is one with a closed set of answers: for example, the answers to [iii] are just "Yes" and "No". By contrast, [liii] has any number of possible answers, and is therefore an open question; similarly with Who attended the meeting?, and so on.

Finally, here is what CGEL says about how acting as adverbial degree modifier. The relative example is [16i].

(b) Adverbial degree modifier

[16]   i  [How old] is your father?                                   [modifier of adjective]
         ii  [How many] children have they got?                [modifier of degree determinative]
        iii  [How seriously] are they taking his threat?      [modifier of adverb]
        iv  How did you like the concert?                             [modifier of verb]

How modifies adjectives, degree determinatives, adverbs, and verbs to question degree, extent, quantity. Only a very small number of verbs (like, enjoy, please, etc.) take how in its degree sense: with other verbs, degree is normally questioned with how much, as in How much do you care about him?

Whatever its category, the word modified by how is always gradable. The presupposition of the question then depends on the nature of the scale involved. Consider:

[17]   a.  How deep is the water?       b.  How shallow is the water?

While [b] presupposes that the water is shallow, [a] does not presuppose that it is deep—only that it has a value on the scale of depth, a value which may or may not fall within the range denoted by the unmodified adjective deep.

                                                                                                                                                   (p. 908)