In a book called Collins English Conversation p.265 there is an example:
I was looking forward to have a rest.
My question is about whether we should use "looking forward to have a rest" or "looking forward to having a rest" ?
In my opinion, we should use "having" after "looking forward to " because we always say "looking forward to hearing from you", so an ing-form of verb should be placed after the phrase " looking forward to".
May someone please explain about the usage for me?
You look forward to something (where "something" must be a noun phrase). So if what you're looking forward to is an activity identified using a verb, you need the "nouny" -ing verb form...
I'm looking forward to having a rest
I look forward to resting
I looked forward to my birthday
etc.
You can tell having a rest is "nouny" because it can function as the subject of a main verb, as in Having a rest is always nice.
I can't find OP's specific cited example I was looking forward to have a rest online, but it's either a misprint or OP has mistranscribed the text - this is not a valid English construction.
Note: It's irrelevant that OP's example happens to use the Past Continuous for was looking forward. It would still be invalid if it had been, say, I looked forward to have a rest.
That is correct. "Looking forward to" is a phrasal verb, and it needs an object. In this case, the object would be the gerund phrase "having a rest," as you rightly deduced. Here's a whole list of phrasal verbs: https://www.englishclub.com/vocabulary/phrasal-verbs-list.htm as well as a link that explains gerunds and gerund phrases: https://owl.english.purdue.edu/owl/resource/627/01/.
If you were to leave the sentence as it is, and try to make it correct, it would be broken up differently. It would read "I was looking forward (in order) to have a rest." In this case, to belongs with have, and it creates a suboordinate infinitive clause. However, that sentence would be very awkward, and borders on nonsense.
