There is one very simple rule about prepositions . And, unlike most rules, this rule has no exceptions.

Rule : A preposition is followed by a "noun ". It is never followed by a verb.

By "noun" we include:

  • noun  (dog, money, love)
  • proper noun (name) (Bangkok, Mary)
  • pronoun  (you, him, us)
  • noun group (my first job)
  • gerund (swimming)

A  preposition cannot be followed by a verb. If we want to follow a preposition by a verb , we must use the "-ing" form which is really a gerund   or  verb   in  noun   form.

Quick Quiz: In the following sentences, why is the preposition "to" followed by a verb? That should be impossible, according to the rule that you have just read.
  • I would like to go now.
  • She used to smoke.
See answerThe answer is that in "I would like to go now" and "She used to smoke", the word "to" is not a preposition. It is part of the infinitive ("to go", "to smoke").

Here are some examples:

subject + verbpreposition"noun"note
The food isonthe table.noun
She livesinJapan.proper noun
Tara is lookingforyou.pronoun
The letter isunderyour blue book.noun group
Pascal is usedtoEnglish people.
She isn't usedtoworking.gerund
I atebeforecoming.

sources : Original Link