A preposition links nouns, pronouns and phrases to other words in a sentence. The word or phrase that the preposition introduces is called the object of the preposition. Prepositions are idiomatic Prepositions are difficult to understand because they do not have precise definitions. Instead, they draw much of their meaning from the noun phrase that they are attached to in a sentence. If you are ever in doubt as to the correct use of a preposition, consult a dictionary or other reference source for proper usage. Prepositions dealing with time, space, position, and direction Often, prepositions are used to situate objects, persons, or events in time and space. a) His book is in the bedroom. The use of the preposition “in” establishes a link between the nouns book and bedroom, specifically telling the reader where the book is located. The object of the preposition is “bedroom.” b) The meeting is at six o’clock. The use of the preposition “at” establishes a link between the meeting and six o’clock, specifically telling the reader what time the meeting will be held. The object of the preposition is the phrase “six o’clock.” c) Common Prepositions: about along with below by inside on over to up above among beneath down inside of onto past toward upon across around beside during into on top of since towards within after at besides for near out through under against before between from next to out of throughout underneath along behind beyond in off outside till until Prepositions dealing with comparisons, exclusions and additions: Another way prepositions may be used to establish relationships between words is to provide comparisons, exclusions and additions. All of these words can be used as transitional words: they let the reader know that you are changing ideas or are changing views about an idea. For example: Most people know smoking is dangerous to one’s health. In spite of this knowledge, many people continue to smoke. All students may go on the field trip, except for those who failed to get their permission slips signed. Common Prepositions: according to concerning excepting of with as despite in addition to on account of without as for due to in spite of regardless of aside from except instead of regarding because of except for like unlike Prepositional Phrases Prepositional phrases are expressions that modify the sentence in which they occur. They perform the role of an adjective or an adverb, providing context for the object, person, or event being described. a) Mary sat by the window. This prepositional phrase is performing the job of an adverb, modifying the verb “sat.” b) The car is behind the house. This prepositional phrase is performing the job of an adjective, modifying the noun “car.” Prepositions and commas If a prepositional phrase occurs at the beginning of a sentence, a comma should be placed immediately following it. a) According to most dentists, you should brush your teeth after every meal. b) Due to our late arrival, we will be unable to meet you for dinner. However, when used later in a sentence, prepositional phrases typically do not need to be set off with a comma. a) We will be unable to meet you for dinner due to our late arrival. Final Note Many professors may suggest that you refrain from ending a sentence with a preposition; this is a suggestion to the style of your writing. It is well to consider that a sentence ending with a preposition is sometimes clumsy, often weak. However, there is no grammar rule that states you can never end a sentence in a preposition.