#1. Some prepositions are homonymous with adverbs and conjunctions.

For instance, the prepositions after and before are homonymous with the adverbs after and before and with the conjunctions after and before.

There is an old saying that if a man has not fallen in love before forty, he had better not fall in love after. (Shaw) (ADVERB)

When he got back to Ann Arbor, he found Savina in a state of excitement because Trasker had heard from Regan after Erik had left. (Wilson) (CONJUNCTION)

“Where do you intend to stay tonight?” she asked after a moment. (Wilson)(PREPOSITION)

The color rushed into Bosinney’s face, but soon receded, leaving it sallow- brown as before. (Galsworthy) (ADVERB)

He did not write to her, and it was almost a year before he began to see her again. (Wilson) (CONJUNCTION)

This letter seemed to afford her peculiar satisfaction; she read it through twice before replying to the landlady. (Mansfield) (PREPOSITION)

Though identical inform, adverbs, prepositions, and conjunctions are different parts of speech. The adverb, unlike the preposition and conjunction, serves as part of the sentence, e. g. after is an adverbial modifier of time, etc.

#2. Some prepositions (on, in, by, over, off, up) are homonymous with post-positions.

A preposition as well as a postposition does not perform any independent function in the sentence. But while a preposition denotes the relation between objects and phenomena, a postposition is part of a composite verb.

A preposition is not usually stressed, while a postposition usually bears the stress.

We’ve got to live on what we earn. (Cronin) (PREPOSITION)

He liked Erik more than any of the assistants the department had taken on in a long time, as much as he could like, one of the younger men. (Wilson) (POSTPOSITION)