A complex preposition is a phrase that consists of two or more words and indicates the relationship between two or more objects in a sentence. For instance, a phrase like "because of" can be used in a sentence such as "We canceled our picnic because of the rain." In this instance, it is used to indicate a causal relationship between the first part of the sentence and the final phrase "the rain." A complex preposition can also consist of three words, like "on top of," and typically serves the same function as a simple or one-word preposition.
The purpose of a preposition in a sentence is typically to connect ideas together by indicating information about their relationships, or to provide an adverbial modifier. Simple prepositions include words like "after" and "on" in sentences like "I'll eat after the game" or "I need the book on the table." A complex preposition functions in much the same way, but simply consists of more than one word used together as a single unit. For example, the phrase "prior to" is used similar to "after" in a sentence like "I'll eat prior to the game."
In this example, the subject of the sentence is "I" while the rest of it is the predicate, which begins with the verb phrase "will eat," expressed as part of the contraction "I'll." The rest of the sentence is a long prepositional phrase that begins with a complex preposition. In this case, it is "prior to," which indicates an order of events occurring, specifically that the subject and action it takes happens before something else. The rest of the prepositional phrase is a simple noun phrase consisting of the definite article "the" and the noun "game."
It is important to keep in mind, "the game" is not an object in the sentence. The verb "eat" is being used, which means that a direct object in the sentence would indicate the item being eaten. Since "the game" is not that item, it is part of the prepositional phrase and not an object in the sentence.
A complex preposition can also consist of three words, and still acts as a single unit. In an example like "The book is on top of the table," the subject is the noun phrase "the book." The predicate begins with the verb "is" and then consists of another long prepositional phrase. In this case, it acts as a subject complement that indicates information about the state or position of the subject. "On top of" is a complex preposition and is followed by the noun phrase "the table."