Diagramming Sentence Modifiers

Sometimes modifiers can modify not just the nouns or verbs that are the heads of their constructions, but entire sentences.  An obvious example is the introductory subordinate clause, which in the syntax of English always modifies the whole main clause.  The comma that always follows the introductory subordinate clause conveys precisely this information about the structure of modification:  the comma indicates that the introductory clause is movable in the sentence, and therefore modifies the whole main  clause--not just some particular part of it.

Single words can function the same way as introductory subordinate clauses--that is, can function to modify the whole main clause of the sentence.  In the traditional grammar, such single words are often called "introductory adverbs" (though they are not adverbial in form), and they should not be confused with coordinating conjunctions.

Words that are adverbial in form, or also prepositional phrases, can modify whole sentences.  Note that the introductory words or phrases set off by commas in the following sentences are, like introductory subordinate clauses, movable in the sentence.

Nouns of direct address and interjections may also be treated as sentence modifiers, as follows.

In all of the examples so far, the sentence modifiers have come at the beginning of the sentence.  The sentence modifiers, however, are movable--that mobility is implied, in fact, in the notion of the "sentence modifier."   When a sentence modifier comes somewhere in the middle of the sentence, it is necessary to draw a bridge in diagramming, as in the following examples.

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