Free modifier

A free modifier is a phrase or clause that can be lifted out of a sentence without breaking it, and usually moved to a different position in it — set off by commas, it adds detail rather than identifying anything.

Sanchez, still in his coat, read the first page twice. Take the bold phrase out and the sentence survives intact. Move it to the front or the end and it still works. That mobility is the test: a free modifier is free because the sentence does not depend on it.

Most of the movable constructions qualify — participial phrases, absolute phrases, appositive phrases, non-restrictive relative clauses, and many adverbial phrases. They are set off by commas, and the commas are the signal to the reader that what follows is addition, not identification.

The opposite case is the bound modifier, which is welded in place and carries no commas.

Why the distinction earns a page: free modifiers are the whole reason a long sentence can stay readable. Because the main clause is complete before they arrive, the reader is never left holding an unfinished thought. This is the principle behind the cumulative sentence, and it is the reason a two-hundred-word sentence built from free modifiers reads faster than a forty-word sentence built from nested clauses.