1. Gerunds and Infinitives
You just have to learn what goes with what...
By Mr Collins

2. It starts a little bit confusing...
Both gerunds and infinitives can be used as the subject or the complement of a sentence. However, as subjects or complements, gerunds usually sound more like normal, spoken English; whereas, infinitives sound more abstract. While gerunds sound more natural and would be more common in everyday English, infinitives emphasize the possibility or potential for something and sound more philosophical. If this sounds confusing, just remember that 90% of the time, you will use a gerund as the subject or complement of a sentence.

3. So what is a Gerund?
A gerund is a verb ending in –ing that is used as a noun.
It can be used as either as a subject, object or complement.
Simply put a gerund is an action being used as a thing or idea.
Imagine a gerund as an activity (a non-physical object), this will help begin you see the difference between the word as a verb and a noun.

4. Making it negative Gerunds can be made negative by adding "not.“
Examples:
He enjoys not working.
The best thing for your health is not smoking.

5. Positioning
A gerund’s position in a sentence depends on what its function is (subject, object or complement).
Examples:
Reading helps students learn English. (Gerund as a subject.)
He enjoys reading for English class. (Gerund as an object.)
Her hobbies include reading. (Gerund as a complement.)

6. Gerund as the subject of a sentence
This position commonly calls for a gerund. While an infinitive is also possible, it is very formal and not common.
Shopping is my favourite hobby.
Working out has really improved my health.

7. Gerund as the object of a verb
This is the one position where both gerunds and infinitives are commonly used. The choice of which to use all depends on the verb. Some common ones are: advise, avoid, enjoy, finish, practise, quit, and suggest.
He enjoyed learning about gerunds.
My teacher suggested studying for the upcoming quiz.

8. Gerund as a Subject complement
First, what is a complement?
Complement is the term used for a word (or words) which are needed to complete the meaning of an expression. Most phrases and clauses will include a complement of some kind. If you can't remove it from your sentence, then it's likely to be a complement.
Now, it is easiest to see a Gerund as a complement if it follows a linking word such as the auxillary verb ‘BE’. If you can replace the linking word with the equals symbol ( =) then it is a complement.
His passion is writing
His Passion = Writing

9. Gerunds follow Prepositions
ALWAYS!!!!
Gerunds are used after prepositions. Most commonly, these are "verb + preposition" combinations.
Examples:
They admitted to committing the crime.
Leslie made up for forgetting my birthday.
He is thinking about studying abroad.

10. Remember that there are many "adjective + preposition" combinations and "noun + preposition" combinations in English as well.
These are also followed by gerunds.
Examples:
Sandy is scared of flying. (adjective + preposition)
Nick is anxious about taking the examination. adj+ prep)
His interest in becoming a professional snowboarder was well known. (noun + preposition)
Thomas' story about seeing a grizzly bear was really exciting. (noun + preposition)
Keeping it simple. Gerunds ALWAYS follow Prepositions

12. Infinitives
Infinitives are the "to" form of the verb. The infinitive form of "learn" is "to learn." You can also use an infinitive as the subject, the complement, or the object of a sentence.
Examples:
•To learn is important. subject of sentence
•The most important thing is to learn. complement of sentence
•He wants to learn. object of sentence

13. Making it negative Infinitives can be made negative by adding "not."
Examples:
•I decided not to go.
•The most important thing is not to give up.

14. When the Infinitive is used
The infintive is used to express purpose
Example:
I’m learning English to help me get a better job.
It is also used after many adjectives (this does not apply to Gerunds)
Examples: delighted, dissapointed, easy, happy, important, lucky, necessary, normal, possible, suprised.

15. Use them both...At your OWN RISK!!
Don’t forget that some verbs take either a gerund or an infinitive with no change in meaning. While students don’t have to worry about these verbs, they should still be pointed out. Some common verbs are: like, love, hate and prefer.
I love eating pasta.
I love to eat pasta.
However, it should be noted it is more common to use Gerunds with these words.

16. But some meanings completely change!!!
Consider this...
He stopped smoking.
He stopped to smoke.
The first suggests he stopped the habit of smoking; whereas, the second says he stopped on the way somewhere to have a cigarette. BIG difference.