Prepositional phrases might be the most misunderstood but essential grammatical construction. I know the grammar books cover other types of phrases, but prepositional phrases are more important for students to recognize and understand.
Prepositional phrases create problems when students are trying to find the subject of a sentence because they end with nouns. Most college students would misidentify the subject in this sentence, for example:
One of my cousins threw a great party on Friday.
I give this sentence to my students at all levels of English composition, and the majority say “cousins” is the subject while a good number say “party” is the subject. One or two know the answer.
The ones who say “party” fall back on the definition of a subject they learned in high school. They will tell me with utter confidence that the sentence is about a party, and a subject of a sentence is what it is about. The sentence is about a party, so that is the subject.
I consider these students to have been well trained in the school of best guesses when it comes to the logical parts of grammar. Unfortunately, they were probably told at one point or another that commas go wherever there is a pause and know that the rules of grammar are really not rules at all, but suggestions.
Such a thought process is not entirely wrong. Most people who know a thing or two about grammar know that many of the “rules” have numerous exceptions. And teachers who have had a linguistics course or two know how arbitrary these “rules” can be and might even be able to name some grammarian from the 18th or 19th century who tried to apply the rules of Latin grammar to come up with rules for English grammar.
The problem is that even if some of the rules are really no more than mannerisms taken to the extreme, they can be quite logical and useful when someone is trying to communicate clearly. Also many of the notions students hold dear about grammar are really notions they should be holding about style.
The students who claim the subject is “cousins” have a mechanical understanding of grammar that tells them the subject is the one who performs the action. These students tend to be closer to the grammatical truth of the matter, but further from a stylistic understanding. When I show the class that “cousins” is part of a prepositional phrase, they tend to catch on pretty quickly to the grammatical logic of the sentence and of prepositional phrases.
Most students catch on to the idea that prepositional phrases are not essential to an independent clause with just a little instruction and practice. Once I have them cross a few prepositional phrases out of a few sentences, they see that the sentence can stand on its own without the clutter.
Prepositional phrases bring up both a grammar issue and a style issue. In grammar, students need to know that grammatical forms can have grammatical functions that are quite different. I am not writing about homonyms or synonyms or how words can have multiple meanings in different contexts. Instead this is about the difference between a word’s or phrases’ form and function. These are a matter of what a word or phrase is as opposed to what a word or phrase does. A verb in an infinitive form, for example, can never function as the main verb of a sentence, but it can function as the subject of the sentence. Here is an example:
To give anything less than your best is to waste the gift. –Steve Prefontaine.
To give is in the infinitive form, but it functions as the subject of the sentence. Students usually see grammar as a matter of identifying parts of speech, but that is only the form aspect of grammar. Knowing who is performing the action or being described through the verb is necessary to knowing the subject of the sentence, and subjects are not parts of speech. They are functions that employ forms to do their work.
An important concept for students is that a phrase can be in the form of a prepositional phrase, but it can function as an adjective or adverb. Prepositional phrases never function as prepositional phrases. That is just their form. But adjectives and adverbs can be both forms and functions. I know there is a high school teacher somewhere who is covering this ground in class and knows this stuff far better than I do, but I have yet to meet a student who understands this distinction.
No matter. Prepositional phrases are of limited use to students when they use them just to make finding the subject of the sentence a little easier, but that use is necessary. Prepositional phrase become meaningful when students see how they can develop their sentences and refine their ideas just by spinning out useful prepositional phrases and developing their sentences with them.