1. The infinitive and the -ing form

           1. . . . The infinitive and the -ing form

We use the to - infinitive:

•  To express purpose e.g. She went to the bakery to buy some bread. 
• after would love, would like, would prefer e.g. I'd love to go to Paris.
• after certain adjetives: glad difficult, happy, sorry etc. e.g. We were glad to meet them again after so many years.
• after certain verbs: advise, agree, appear, decide, expect, hope, learn, manage, offer,  promise, refuse, seem, teach, want, etc. e.g. She managed to catch the train on time. We promised to write home every day.
• in the expressions: to tell you the truth, to begin with, to be honest, to start with, to sum up, etc. e.g. To tell you the truth, I don't like vanilla ice-cream.

We use the infinitive without to:

• after modal verbs: can, could, may, might, will, would, must etc. e.g. I must see the doctor immediately. Can I open the window?
• after feel, hear, make, late etc. e.g. "I will let you go to the party if you promise to be back by 10.30" Mother said.

We used the -ing form:

• as a noun e.g. Playing chess is very exciting.
• after love, like, dislike, hate, enjoy, prefer etc. e.g. I hate cooking dinner. I enjoy working in the garden. 
• after prepositions e.g. He left without taking his umbrella.
• after certain verbs: avoid, admit, fancy, finish, forgive, imagine, keep(=continue), mind (=object to), regret, suggest etc. e.g. He suggested visiting the modern art museum. They kept dancing until the clock struck twelve.
• after the expressions: I'm busy, it's no use, it's (not) worth, what's the use of, can't help, can't stand, there's no point (in), look forward to, what about...? how about ... ? etc. e.g. It's no use trying to repair that bicycle. We had a great time and we're looking forward to seeing you again soon.

Note: certain verbs may be followed by either the to-infinitive or the -ing form. In this case, however, there is a change in meaning. 

• FORGET

          forget + to-infinitive = not remember e.g. I'm sorry I forgot to turn the light off.

          forget + -ing form = forget a past event e.g. I will never forget winning the first prize.

• REMEMBER

          remember + to-infinitive = remember to do something e.g. He remember to turn off the gas.

          remember + -ing form = recall a past event e.g. I don't remember visiting the zoo.

• TRY 

          try + to-infinitive = do one's best, attempt e.g. The climbers tried to reach the mountain peak buy they couldn't.

          try + -ing form = do something as an experiment e.g. Why don't you try adding some tomato sause? It might taste better.

• STOP

         srop + to-infinitive = stop for a while in order to do something else. e.g. The students stopped to have a break.

         stop + -ing form = finish, end e.g. When the president came in everybody stopped talking.

• REGRET

         regret  + to-infinitive = be sorry e.g. I regret to inform you that we cannot accept your application.

         regret + -ing form = have second thoughts about something that one has already done. e.g. I regret talking to her so rudely.