Is it acceptable to use a free modifier at the beginning of a clause to signify a cause for the action expressed by the clause, instead of using a subordinate clause in the same place beginning with "because", "since", etc? Or do free modifiers, when beginning with participles, only signify action occurring at the same time as that expressed by the clause it modifies? Exactly what is the function and meaning of free modifiers?
A free modifier is itself a clause, not typically just a word. It's "free" because it can head a sentence, conclude a sentence, or appear as an interjection without its placement altering the meaning or sense of the sentence. Ones beginning with participles do not necessarily only refer to simultaneous action. They can certainly speak to causality: Having chosen from the three candidates, Trish called them in separately to give them the news. But they certainly can also speak to simultaneity, though it's often of a more figurative, general nature rather than specifically this action, right now. Ones that key off of participles tend to serve as adverbial modifiers, modifying the action in the main clause. Others, like absolute and resumptive, are adjectival in nature and modify a noun within the main clause.
