Cambridge Grammar of English Hardback with cd-rom a comprehensive Guide

Peripheral elements

Adjuncts are normally regarded as peripheral elements in the clause; they are

always optional, they are the most mobile elements (they can occupy different

positions), and they do not determine what else must occur in the clause. 

492 | Introduction to sentences and clauses

Cambridge Grammar of English

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Adjuncts are even more flexible than objects and predicative complements, and

may occur in a variety of positions:

In the morning we had to pretend nothing happened.

(adjunct in front position; also possible: We had to pretend nothing happened

in the morning.)

We 

sometimes go to Rochester.

(adjunct between subject and verb; also possible: Sometimes we go to

Rochester.)

That young guy seems to deliver the post 

quite often these days.

(adjuncts in final position; also possible: Quite often that young guy seems to

deliver the post these days./These days that young guy seems to deliver the post

quite often.)