Constructions of the form 'He has committed I don't know how many crimes.'

What is the grammar (or syntax, if you will) of constructions of the form of the below sentence?

He has committed I don't know how many crimes.

In this sentence, for example, what is the grammatical role of the clause 'I don't know how many crimes'. Is it the object of the verb 'committed'? What type of clause is it?

This is a fairly well accepted construction which, however does not fit into the traditional scheme of things in the grammar of English. What can be thought about it from the knowledgeable point of view of grammarians is given a fundamental introduction in section 17.112 of the Comprehensive Grammar of the English language (Quirk et al, 1985). If one needs to refer to the structure preceding such noun phrases as "crimes" in the query, one says that the structure can be considered either as involving premodification by a sentence or that the noun phrase is the object (of know) in an embedded nominal clause. The nature of this premodification is more or less adverbial; the premodification of nouns by regular adverbs is rather rare (an away game, the then chairman, in after years, …).

(CoGEL § 17.112) Premodification by sentence

What [can be] said of adverb phrases [as pertains to premodification of noun phrases] applies to premodification by a sentence :

♦ (?) I visited his what do you call it cottage [ cf: What do you call it when a cottage has walls made from overlapping pieces of'timber? Clapboard] [user LPH: the interrogation point means that native speakers do not find this type of sentence fully acceptable.]

A few institutionalized examples retain a colloquial or slang flavour: a whodunit story is one about crime, and the nonstandard grammar or spelling are preserved as part of the ironic slang. Do-it-yourself as in a do-it-yourself job has become so often used as to pass out of the area of slang (and sometimes be reduced to DIY).

Somewhat more widely acceptable are noun phrases which can be interpreted either as having a sentence as premodifier or as being object (usually of know) in an embedded nominal clause:

♦ He asked I don't know HÒW many people. [user LPH: "how" carries nuclear stress.] [1]
♦ He asked I don't KNÒW how many people. [1a]

With either intonation, the meaning is 'He asked a relatively large number of people, though I don't know precisely how many'. The meaning is somewhat different if the sentence is reordered, enforcing a different grammatical structure:

♦ I don't know how many people he asked. ['I don't know the number of people he asked.']

For the most part, however, sentence premodifiers have an air of the outrageous and improvised. Part of a political leader's election campaign was described by a journalist as

today's meet the people (if they can find you) tour

Far more remarkable is the following quotation from a literary comment in which the sentence premodification itself has highly irregular and sophisticated punctuation to convey highly irregular coordination devices:

     His other comments ignore. . . the obvious fallacies inherent in the
       'But the poem (play, novel) was meant to be tedious/pretentious/pointless' line of critical argument.

Note: There is matter for disagreement among grammarians in the assertion that such constructions as "away game" and "then chairman" show examples of premodification by adverbs. The SOED dictionary lists "away" and "then" as adjectives and gives the example "his then wife"; this approach appears to be preferable.

These types of constructions are actually covered in CGEL (Ch. 11 Content clauses and reported speech, section 5.3.4, p. 984):

A distinction needs to be drawn between the following constructions:

i: He made some mistakes, though I don’t know how many.

ii: He made I don’t know how many mistakes.

In [i] how many is a reduced interrogative clause functioning as complement to know. This differs from the constructions we have been discussing only in the reduction of the interrogative clause; it is interpreted anaphorically as “how many mistakes he made”.

In [ii], however, there is no ellipsis, and how many mistakes is not an interrogative clause. It means very much the same as "I don’t know how many mistakes he made", and its form seems in some way derivative from the latter. But clearly made is the verb of the matrix clause and the proposition that he made some mistakes is the main assertion, not backgrounded information; and there is an implicature that he made a large number of mistakes. Syntactically, I don’t know how many mistakes must be an object NP with mistakes as head; I don’t know functions as an irregular type of modifier to how.

A variant of I don’t know is God knows. These modifiers occur with most of the interrogative words (though not why) – compare They’re inviting God knows who to the reception.