In the sentence, "I have been sick for a week", I is the nominative, have been is the copula, sick is an adjective and for a week is an adverbial phrase.

Does the adverbial phrase "for a week" modify the adjective "sick", or is it "standalone"?

Would the answer change if you moved the adverbial phrase to the front, so that the sentence reads: "For a week, I have been sick"?


“I have been sick for a week.”

This is a Simple Sentence, which means it has only one independent clause containing a single subject and a single verb. The verb phrase “have been” is Present Perfect with the helping verb [have] and main verb [been] together acting as a single unit: a verb. It is a linking verb.

Because the Adverb Prepositional Phrase “for a week” answers “How long?” it is acting as an adverb, of which adverbs modify adjectives, verbs, and other adverbs. So, in your sentence “for a week” is modifying, and can only modify, the verb phrase “have been.” The reason for this is that the verb phrase "have been" is in tense, giving reference to time, and the adjective "sick" does not have anything to do with time.


I / have been / sick / for a week

Subject / Present Perfect verb phrase / predicate adjective / adverb prepositional phrase

Adverbs, and adverbial phrases are pretty versatile and can be found in different places in a sentence, AND still modify the word it is intended to modify:

For a week, I have been sick. OR I have been, for a week, sick. [the commas are used for clarity and not to offset the phrase from the sentence because it is nonessential (the sentence can survive without it and still be meaningful: I have been sick.)]

Reference: John E. Warriner. Warriner’s English Grammar and Composition. Third Course. Liberty Edition. Orlando, Florida: Harcourt, Brace, and Jovanovich. 1986.


"I have been sick [for a week]".

The preposition phrase "for a week" does not modify "sick", but is a duration adjunct (adverbial) in clause structure.

It does not in some way add meaning to (i.e. modify) the adjective "sick" like some PPs would, as in "I've been sick with a fever", or degree adverbs like "terribly" or "very"; rather, it states the duration of your having been sick.

As you noticed, it is moveable (cf. "For a week, I've been sick") and of course it is omissible.

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    Which means it "modifies" the entire clause, or the entire verb phrase, or any subordinate verb phrase within it. I.e, modification is of little importance at the clausal level. – John Lawler Aug 28 '16 at 15:28

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