A "preposition" is a word, typically used in front of nouns or pronouns, that shows the relationship between the noun or pronoun and the other words in a sentence, conveying agency, comparison, direction or place. It can also convey possession, purpose, source or time. Examples of prepositions include "after," "in," "to," "on" and "with."
A preposition is a traditional part of speech belonging to a closed word class, meaning new ones rarely enter the language. Of the about 100 single-word prepositions in English, some stand alone, and some are complex preposition phrases with two or more words. The phrase "in addition to" is an example of a complex preposition. When the preposition is followed by an object, the resulting word group is known as a prepositional phrase. In the sentence "Alex put the horse before the cart," the phrase "before the cart" is a prepositional phrase.
Most commonly, prepositions show location, direction or time, but prepositions also convey agency, comparison, possession and source. Some prepositions function as other parts of speech, such as subordinating conjunctions when followed by a clause, or adverbs when they modify verbs. Similarly, some words have the form of prepositions but do not have the same function. For example, depending on the context, the preposition "in" could be a preposition of place or a particle.