英语文法: “look forward to” + “doing”
Source: Zhihu
(prepared by: alexcwlin; edited by: Adam Lam)

Question:
为什么 look forward to 后面一定要接 doing，其中的 doing 是非谓语动词吗？

alexcwlin comments:
The entire phrase “look forward to” is a Transitive Phrasal Verb:

Encarta Dictionary:


What usually follows a Transitive Verb is a Noun or a Nominal (Verb-form Noun) as Object of the Transitive Verb.

Here are the choices under consideration:

1.     Gerund:
I look forward to seeing you.
Comment: Here “seeing” is a Gerund (Verb-form Noun), and it’s correct.

2.     Noun.
I look forward to the trip.
Comment: Here the Noun Phrase “the trip” is fine as Object of the Transitive Verb.

3.     Infinitive
I look forward to to see you.
Comment: An Infinitive can be used as a Verb-form Noun and therefore grammatically this sentence is fine. However, it looks odd to have 2 “to’s” one after another and therefore I haven’t seen it used that way.

4.     Participles, Adjective and Adverb
(These are not Noun forms and therefore cannot be used as Object of the Transitive Verb “look forward to”).

Conclusion:
In addition to “doing”, you can also follow “look forward to” with a Noun/Noun Phrase.