A preposition is a word placed before a noun or a pronoun to form a phrase that modifies another word in the sentence. The prepositional phrase functions as an adjective or an adverb.
To the summit functions as an adjective modifying the noun road; past craters functions as an adverb modifying the verb travels; from an extinct volcano functions as an adjective modifying the noun craters. (For more on prepositional phrases, see 42a.)
English has a limited number of prepositions. The most common are included in the following list.
about | below | from | outside | underneath |
above | beside | in | over | unlike |
across | besides | inside | past | until |
after | between | into | plus | unto |
against | beyond | like | round | up |
along | but | near | since | upon |
among | by | next | than | with |
around | despite | of | through | within |
as | down | off | throughout | without |
at | during | on | to | |
before | except | onto | toward | |
behind | for | out | under |
Some prepositions are more than one word long. Along with, as well as, in addition to, next to, and rather than are examples.