Gerunds (-ing forms) after prepositions

When we put a verb after a preposition, we normally use an -ing form, not an infinitive.

§  I am fond of watching movies. (NOT I am fond of to watch movies.) 

§  John was arrested for stealing a policeman's helmet. (NOT ... for to steal ...)

§  Can you talk without opening your mouth? 

§  I am thinking of writing a novel. 

§  You must abstain from talking to such people. 

§  We got the job finished by burning the midnight oil.

§  We look forward to hearing from you.

To as a preposition

To can be an infinitive marker (e.g. to work, to laugh). It can also be a preposition. When to is a preposition, it is followed by either a noun or the -ing form of a verb, but not normally by the infinitive. Common expressions in which this happens are look forward to, object to, used to, prefer to, get round to, in addition to.

Compare:

§  I look forward to his next visit. (noun)

§  I look forward to hearing from you. (NOT I look forward to hear from you.) 

§  I prefer the country to the city. (noun)

§  I prefer swimming to walking.

§  I am used to waiting for buses. (NOT I am used to wait for buses.) 

§  They objected to our entering the room. 

§  I object to working on Sundays.