Строй современного английского языка

LOOSE PARTS
The theory of loose parts of the sentence is another backward element of syntactic theory. Even the terminology in this field is far from certain. The term "loose" is used in English grammars chiefly with reference to the apposition: close apposition and loose apposition are two notions opposed to each other in grammatical theory. Another term which may be used is "detached": detached attributes, detached adverbial modifiers, and so forth. We will use the term "loose".
By loose parts of the sentence we mean such parts as are less intimately connected with the rest of the sentence and have some sort of independence, which finds its expression in the intonation and, in writing, in the punctuation.
The question now is, what parts of the sentence can be loose. The main parts, subject and predicate, apparently cannot be loose, as they form the backbone of the sentence from which other parts may be "detached". Objects cannot apparently be loose either. So the following parts remain: attributes, adverbial modifiers, appositions, and parentheses.