Consider the following sentence:

We had to go to get a book.

This is how I identify each word or group of words to its corresponding part of speech:

  • We is the subject of the sentence.
  • had is the auxiliary verb, the sentence is in past tense. The sentence could end here and it is still grammatically correct.
  • to go is an infinitive acting as an adverb modifying the verb had. The sentence could also end here and still be grammatically correct.
  • to get a book this is my question. How should I dissect this? If the sentence ends at to get a person would ask "to get what?" so the noun a book is a restrictive component to the word to get. Is this an infinitive phrase? A compound noun? I don't think it is a preposition either. Did I wrongly approach this structure?
  • You can't analyse it like that. "To go" is not a constituent, and in any case it would not be a modifier of "had". "A book" is object of "get".
    – BillJ
    Commented May 30, 2020 at 17:35

2 Answers 2


We had [to go [to get a book]].

Preliminary point: most speakers treat stative "have" as a lexical verb, but some treat it as an auxiliary.

The sentence consists of a main clause (the sentence as a whole) and two embedded subordinate clauses, as bracketed.

"Have" is a catenative verb and the subordinate clause "to go to get a book" is its complement.

The second subordinate clause, "to get a book", is a purpose adjunct in clause structure. "A book" is object of "get".


"Have to" is used in the sense of "must" to mean something is obligatory. "Must" is an auxiliary verb; but "have" is a main verb.

e.g., I must do it. (Subject + auxiliary verb + main verb + object)

= I have to to do it. (Subject + main verb + to-infinitive)

I will have to do it (Subject + auxiliary verb + main verb + to-infinitive).

"We had to go to get a book."

Here, had is not an auxiliary verb.

We = subject

had = main verb

to go = to-infinitive

(had to go = were obliged to go.)

to get a book = infinitive phrase showing purpose.

  • 2
    It's worth noting that in principke there's no limit to the number of "infinitive phrase showing purpose" elements that can be chained together in such contexts. We had to go to get a book to give to him to help him pass his exam to go to university... Personally, I'd also add that for many if not most native speakers, had here would be pronounced hat (and the Present.Tense versions written has / have would be enunciated with a "hard s / f" as hass / haff). Commented May 30, 2020 at 16:41
  • Exactly. We can use such "infinitive phrases showing purpose" one after another / successively. Commented May 30, 2020 at 16:44
  • "Have" is an auxiliary verb for some speakers.
    – BillJ
    Commented May 30, 2020 at 16:51
  • 1
    "We have gone there". Here, "have" is an auxiliary verb. "We have to go there". Here, "have" is a main verb. Commented May 30, 2020 at 18:24
  • No: In "We have to go there", "have" can (for some speakers) be an auxiliary verb. The difference becomes apparent in interrogatives. Auxiliary "have" inverts with the subject ("Have we to go there?"), while lexical "have" requires do support ("Do we have to go there?").
    – BillJ
    Commented May 30, 2020 at 18:35

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