Here, I read that verbs that follow prepositions must always be used as conjugated. I can barely find anything on the web that mentions this rule, besides the link I provided.
This rule seems to be true almost all of the time. So I had my student come up with some sentences that showed this. For example,
He generally showers after playing tennis.
I'm looking forward to having dinner with the Smiths.
He's daydreaming about skiing in the Andes.
But then he said:
I have to writing a report.
This I know isn't grammatically correct.
It should be: "I have to write a report."
So is the rule I found only good most of the time? Is it an actual rule, or did someone just make it up and post it on their English club page? Or is "to" not a preposition in "I have to...". Spot-on This is the to-infinitive, not a preposition.
Please, can anyone shed some light on my doubts?
Thanks in advance.