The sentences we write have to have the right words for the ideas we want to express. But having the right words is not enough alone. We then have to arrange those words into accepted patterns that bring our ideas across in just the right way and manner and style to the reader we have in mind.
A simple sentence, a very common pattern, is made up of one and only one independent clause—one subject connected to one predicate, those two components together making a complete thought: I have read your proposal. The predicate is that part of a clause that contains the verb and everything else that goes with it to round out the thought we want to communicate. A compound sentence, another common pattern, combines two or more such complete clauses in order to assert more thoughts within the compass of one sentence: I have read your proposal and I will send it to the committee for approval. Both the simple and compound sentence are basic choices for the writer, so basic, in fact, that without varying their structure from time to time, our style will appear limited and predictable and less interesting than it could otherwise be.
So what to do? Independent clauses, the kind that make up both simple and compound sentences, are not the only choice we have in composing our word patterns. Phrases are also available to us, and it’s of real, practical importance to understand the difference. If a clause is a group of words with a subject and predicate, a phrase is a group of words without a subject and predicate. A clause asserts a thought; it says this is this or that is not that. It can be forthright, downright, straightforward, frank, clear. A phrase, though, does not assert a thought; it suggests one. The sentence I will send it to the committee for approval contains one clause (I will send it) and two phrases (to the committee and for approval). The phrase to the committee suggests the complete thought the committee will receive the proposal, and that is a clause. Likewise, the phrase for approval implies the complete thought I will recommend approval, and that too is now a complete and declarative thought.
Phrases, then, abbreviate our thinking, and that, in the right place at the right time, can be a good thing, because all that declaring that a clause undertakes can become a bit much. Phrases, of course, come in all shapes and sizes; the two we just looked at are called prepositional phrases. One more, a particularly interesting one, is the participial phrase. I say interesting because the participle is a sophisticated piece of grammatical machinery. It combines the functions of both an adjective and a verb, and in doing so, it both modifies a noun and says something about the circumstances of the main thought—circumstances, after all, are just what verbs create. So if, from time to time, we can convert one independent thought of a compound sentence into a participial phrase, we will have found a way to write in a style that more closely reflects the real complexity of our human experience.
If we take, then, the compound sentence I have read your proposal and I will send it to the committee for approval and revise the first clause into a participial phrase, we would produce this revision: Having read your proposal, I will send it to the committee for approval. The phrase having read constitutes the participle, and that entire participial phrase suggests to the reader something about the circumstances that preceded my sending the proposal to the committee. They suggest what happened before I sent the proposal, and with that suggest also the reason I sent it on—which is then made explicit in the phrase for approval later in the main clause. That suggestion and delay in the opening phrase bring interest to the sentence because we humans do not like unsatisfied possibilities; we like completion, resolution, conclusion, and we are pleased when we read them in a sentence.
There is, though, one pitfall to be wary of with such opening participial phrases. Participles, we agreed, are adjectives, and so they must and will modify the subject of the following main clause; this is so because participles, as we noted, also point to the circumstances of the main action, and the subject is the one who brings that action about. The danger is that we put as a subject some noun or pronoun that is logically not correct: Having read your proposal, it will no doubt be approved. The subject pronoun it refers to the proposal, but the proposal has read, we can be assured, nothing at all. I have read the proposal, but that logical subject appears nowhere in this incorrect construction. Thus, we have to return to our original version: Having read your proposal, I will send it to the committee for approval. This is a very common error to be on guard for in our rough drafts.
All of which is to say, clauses state and phrases abbreviate. Using the two deftly can bring a subtle shade of interesting color to the sentences we compose.