Every word has a form (what it looks like) and a function (what it does). Prepositions are words like, up, down, over, under, around (i.e., anything a cat can do). When a preposition heads a phrase, the phrase is called a prepositional phrase, like this,
EX: on the street
EX: under the table
EX: to the store
If a prepositonal phrase answers the question Where? or When? or How? or Why?, it functions as an adverbial phrase. For example,
EX: They went to the library. Where?
EX: The bus comes at 5:00. When?
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A prepositional phrase starts with a preposition and ends with a pronoun, noun or noun phrase. Most adverbial phrases are prepositional phrases functioning as an adverb, modifying a verb, an adverb and an adjective. But there are some prepositional phrases that function as an adjective phrase, not as an adverb;for example, 'I want to see the man in blue trousers'. 'In blue trousers' is a prepositional phrase functioning as an adjectival phrase modifying the noun 'man'. Another difference is that not all adverbial phrases are derived from prepositional phrases. For example, 'I saw him the other day'; the phrase 'the other day' is an adverbial phrase modifying the verb 'saw'
Best Wishes
المفضلات